JPS63114282A - Superconducting switching element - Google Patents

Abstract

PURPOSE:To obtain a high current amplification factor, by contacting a thin superconductor film with a thin normal conductor film, and selecting the value of a transfer length so that it is less than the thickness of the thin superconductor film. CONSTITUTION:The value of a transfer length (Lt) is expressed by an expression Lt=(Rc/R(-))<1/2>, where Rc is a unit area contact resistance between a thin superconductor film 5 and a thin normal conductor film 6, and R(-) is the surface resistance of the thin normal conductor film 6. The value Lt is selected to be the thickness (d) or less of the thin superconductor film 5. When, e.g., 10<-9>OMEGAcm<2> is obtained as the contact resistance Rc and the surface resistance R(-) is 10OMEGA/square, the value of LT is 0.1 mum, which is very small. Since the Lt is very small, the current between the thin superconductor film 5 and the thin normal conductor film 6 flows in an extremely concentrated manner and a current density is small, the parameter of the thin superconductor film 5 is a superconductivity order can be made small. The superconducting characteristics of the thin superconductor film 5 can be weakened. Thus a high amplification factor can be obtained.

Description

[Detailed Description of the Invention] [Summary] The present invention provides an electronic switching element that uses superconductivity. While bringing the thin film into contact with the normal conducting W/J film,
By selecting the value of the so-called transfer length to be less than or equal to the thickness of the superconducting thin film, a high current amplification factor can be obtained.

[Industrial application field]

The present invention relates to a superconducting switching device, and more particularly to an electronic switching device using superconductivity.

Superconductivity provides an ideal conductor for resistor gaps, which is advantageous for creating low-power switching circuits. To realize such a switching circuit, a superconducting switching element with a high current amplification factor is required.

[Conventional technology]

An example of the structure of a conventional superconducting switching circuit is shown in Figure 3 (
R diagram). In the figure, 1 and 2 are superconducting Ti electrodes, and an extremely thin insulating film 3 is interposed between them as a tunnel barrier.

This superconducting switching element is a tunnel-type Josephson device, and the superconducting electrode 1 is cooled to an extremely low temperature.
When a current is passed between R and 2, when the current is below the threshold value, no voltage is generated and the superconducting state is maintained, and when the current is above the threshold value, a voltage is generated and the superconducting state is switched.

(Problem to be solved by the invention) Since a Josephson element is essentially a two-terminal element, it has no directionality, and in order to obtain a current amplification factor, a circuit that combines multiple Josephson elements is used. . However, the current amplification factor obtained with such a circuit is only several times higher at most. This is because it is necessary to provide a margin in the circuit design to prevent the circuit from malfunctioning due to variations in Josephson elements and noise.

As described above, the Josephson element, which is a conventional superconducting switching element, has the problem that it is difficult to realize a circuit with a large current amplification factor, which makes it inconvenient to design a circuit with complex functions. was there.

The present invention was created in view of the above points, and an object of the present invention is to provide a superconducting switching element with a large current amplification factor.

[Means for solving problems]

FIGS. 1A and 1B are a side view and a plan view, respectively, showing the basic structure of the present invention. In the figure, 5 is a superconducting thin film and 6 is a normal conducting thin film. Superconducting thin film 5 and conducting thin film II
! An insulating film (for example, 5fOz) 3 (not shown in FIG. 1(A)) shown with diagonal lines in FIG. 1(B) is provided between J6 and the insulating film. A part of the thin film 2 of the transmission 34 is brought into contact with the superconducting film 5 through a window 8 formed in the superconducting film 7.

Here, the unit surface 8 between the superconducting thin film 5 and the normal conducting thin film 6 is
! 1. If the contact resistance is RC and the sheet resistance of the normal conductive thin film 6 is R6, then the value of 1-t expressed by Lt - (πτ; γW) is selected to be less than or equal to the thickness d of the superconducting thin film 5. There is.

[Effect]

A superconducting current is passed between both ends of the superconducting thin film 5, and a current is supplied from one end of the normal conducting thin film 6. When a current is applied to the superconducting thin film 5 from one end of the normal conducting thin film 6, the current flows in a concentrated manner in an extremely narrow region 9 where the two thin films 5 and 6 are in contact.

The width of the region 9 into which the above-mentioned current is injected is called a transfer length, and is given by the above-mentioned equation of LT.

Here, if the contact resistance Rc is, for example, 10<-9 >[Omega]d, and the surface resistance R8 is 1 o[Omega]/mouth, then the value of LT is an extremely small value of 0.1 [mu]m.

Therefore, L and T are extremely small and superconducting i1! II5
Since the current flows between the normal conductive thin film 6 and the superconducting thin film 6 in an extremely concentrated manner, and the current density is small, the superconducting order parameter of the superconducting thin film 5 can be made small, and the superconducting properties of the superconducting thin film 5 can be reduced. can be weakened.

Note that when the current flowing between the conductive thin film WA6 and the superconducting thin film 5 exceeds a threshold value, the superconducting it'la5 switches to a voltage state.

〔Example〕

FIG. 2 is a cross-sectional view of the structure of one embodiment of the present invention.

In the figure, 11 is a superconducting thin film made of niobium (Nb). Also, 12 is Joden 1'? For aFJ, for example, the film thickness is 11
00n molybdenum (Mo).

Words are weak! II; A part of 412 is in contact with the superconducting thin film 11 soil, and the other part is in contact with the insulating film 13 made of 5 tOz deposited on the superconducting d film 7 by sputtering or the like. . Further, both ends 11a, 1 of the superconducting thin film 11
The film thickness of 1b is 1 μm, whereas the film thickness of the contact portion with normal conductive thin film 12 is formed to be extremely thin, for example, 200 nm, and a current is passed between both ends 11a and 11b.

Further, the conductive thin film g112 is connected to the superconducting thin film 14 as an extraction electrode, and a current is supplied through the superconducting thin film 14.

When a current is supplied to normal conduction Mli12, Genden S thin WA1
A current is injected into the superconducting thin film 11 as a control current through an extremely narrow region 2. As a result, the superconducting thin film 11
Since the superconducting order parameter of can be made small, the magnitude of the superconducting current that can be passed between the terminals 11a and 11b can be reduced to almost zero with the control current having a small value. Therefore, the current that should be passed through the normal conduction membrane 12 is:
When this current is zero, it is easy to make it 1/10 or less of the maximum value of the super low current that can flow between the terminals 11a and 11b.

Note that the present invention is not limited to the above embodiments, and the value of the transfer length Lt is usually 1 μm or less, but may be as long as the thickness d of the superconducting thin film 5 or less.

〔Effect of the invention〕

As described above, according to the present invention, a superconductor **a and a normal conductive thin film are brought into contact with each other so that current flows concentrated in an extremely narrow area, so that the superconducting order parameter of the superconducting thin film is reduced. Therefore, the superconducting properties of the Genden 34 thin film can be determined using the control current (current flowing through the normal conducting thin film to the superconducting thin film).
It is possible to make a large change with a small change in , and therefore a high current amplification factor can be obtained, and the transfer length Lt is determined by the contact resistance RC and the surface resistance R.

Since the contact area between the normal conducting thin film and the superconducting thin film ++a can be relatively large, it is possible to increase the current density of the injected current without performing ultra-precision machining with submicron precision. It has certain characteristics.

[Brief explanation of the drawing]

FIG. 1 is a structural diagram of the principle of the present invention, FIG. 2 is a structural sectional view showing an embodiment of the present invention, and FIG. 3 is a perspective view showing an example of a conventional superconducting switching element. In the figure, 5.11.14 is a superconducting thin film, 6.12 is a normal conducting film, 7.13 is an insulating film, 9 is a region where current is injected, and d is the thickness of the superconducting thin film. Principle structural diagram of the present invention Figure 1 Structural sectional view of an embodiment of the present invention Figure 2 Figure 3

Claims (1)

[Claims] A superconducting thin film (5) through which a current is passed between both ends thereof, and a portion of which is in contact with the superconducting thin film (5), and a current is passed through the corresponding contact portion from one end of the superconducting thin film (5). The normal conducting thin film (6) and the following formula Lt=√(Rc/Ro) (where Rc is the superconducting thin film (5) and the normal conducting thin film (6)
) is the unit area contact resistance, Ro, of the normal conducting thin film (6
) is the sheet resistance of the superconducting thin film (5).
d) A superconducting switching element characterized by being configured with the following values selected.