JPS5829637B2 - Superconducting multi-terminal device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a superconducting multi-terminal element in which tunneling current can be directly controlled by electrical and optical signals.

A superconducting device represented by a Josephson junction device has 10
Its basic precept is a two-terminal device that utilizes the characteristics of tunnel current passing through an insulating layer with a thickness of about A, and the tunnel current is controlled indirectly using the magnetic field induced by a third current flowing near the junction. The structure is complicated because it goes to
There were drawbacks such as difficulty in applying bias to the nonlinear part.

This will be further explained with reference to the drawings.

FIG. 1 shows the basic structure of a Josephson element commonly used at present.

In this figure, 1 is the substrate, 2 and 3 are superconducting electrodes, and 4
is an insulating film existing between the two superconducting electrodes 2 and 3, which is usually an oxide film or a nitride film, and has a thickness of about IOA or less.

An insulating layer 5 is formed on the surface of the superconducting electrode 2.3, and a control electrode 6 made of a normal conducting metal is further provided thereon.

In the conventional Josephson element having such a configuration, the thickness necessary to cause the tunnel effect of the above-mentioned insulating film 40 is I.
It is below the level of OA, and deterioration of characteristics due to flatness such as pinholes and hillocks on the film surface often becomes a drawback in production.

When this type of Josephson element is used for switching, it is necessary to further provide a current path through the insulating layer 5, that is, a control electrode 6, and the magnetic field induced by the current flowing through the control electrode 6 , has a complex structure due to the switching of the bonding surface, and its operation is based on turning on and off using a hysteresis loop.

The present invention provides a novel superconducting multi-terminal device that solves the structural and operational drawbacks of the conventional Josephson device, and instead of the conventional insulating layer, single crystal or polycrystalline
Alternatively, an amorphous semiconductor thin film or semimetallic thin film can be used. By directly applying electrical or optical signals to these semiconductor thin films or semimetallic thin films, the phase coupling state between the superconducting electrodes can be changed by an external signal. It is characterized by controlling the current.

This invention will be explained below. FIGS. 2 to 8 all show embodiments of the present invention.

Referring to FIG. 2, reference numeral 1 denotes a substrate, which is made of a semiconductor, glass, dielectric crystal, or the like that becomes insulating in a temperature range below the superconducting transition temperature of the superconducting material used.

A pair of superconducting electrodes 2 and 3 are made of a material that exhibits superconductivity in the same temperature range on this substrate 1, and a control electrode 7 made of a crystalline or amorphous semiconductor or semimetal is formed between them.
will be established.

The distance between the superconducting electrodes 2 and 3 is several times the coherence length or less, and the third control electrode 7 made of a semiconductor or metalloid is located within this distance.

It is also possible to insert a superconducting substance or a normal conducting metal into a part of the control electrode 7, but in this case as well, it is assumed that both the superconducting electrodes 2 and 3 are connected via a semiconductor or a semimetal.

Next, the operating principle of the above embodiment will be explained.

Since the control electrode 7 used instead of the conventional insulating film 4 (FIG. 1) is a semiconductor thin film or a semi-metallic thin film, electron pairs (Cooper pair) passing through these materials by tunnel current. The coherent length of is longer than that of an insulating film.

Therefore, the thickness of the control electrode 7 made of the above-mentioned material provided between the superconducting electrodes 2 and 3 is set to several times the coherent length or less.
Specifically, the voltage is several hundred A or less, and the width and height of the short key electrode formed between one of the superconducting electrodes 2 and 3 and the control electrode T are controlled by the voltage applied to the control electrode 7. By injecting a current into the superconducting electrodes 2 and 3 from the
, 3 controls the tunnel current based on the electron pairs flowing between them.

This embodiment has a convenient configuration when manufacturing using an epitaxially grown semiconductor substrate or the like, and uses the semiconductor portion left by etching and uses it as a control electrode by applying an electric field or the like directly to the semiconductor portion.

FIGS. 3 to 8 show other configuration examples of the present invention, respectively.

In FIG. 3, the control electrode 7 is manufactured by a process of growing or depositing a semiconductor or metalloid after the superconducting electrode 2.3 is deposited.

, FIG. 4 is manufactured by the process shown in FIG. I hope that the gap between the superconducting electrodes 2 and 30 will be wider due to the intervention.
, it has the advantage of improved switching sharpness.

In FIG. 5, after the superconducting electrodes 2, 3 and the control electrode 8 are vapor-deposited, a semiconductor or semi-metal is grown or vapor-deposited to form the control electrode 7, and a control signal is applied to the control electrode 8 for use.

The characteristics are similar to the embodiment shown in FIG.

The device shown in FIG. 6 is manufactured using the same manufacturing process as that shown in FIG. 3, and the control electrode 8 is further formed by vapor deposition of a superconductor.

In this case, the distance between the superconducting electrodes 2 and 3 does not have to be about the coherent length, and the thickness of the semiconductor or semi-metal film between the superconducting electrode 2 and the control electrode 8 and between the button and the control electrode 8 and the superconducting electrode 30 is the coherent length. It is sufficient as long as it is of a certain extent.

FIG. 7 has the advantage that the control electrode 7 made of a semiconductor or semi-metallic film only needs to have a film thickness on the order of the coherent length, and that it is the simplest to manufacture because it does not require the formation of bumps by fine etching.

FIG. 8 is a basic plan view of the embodiment shown in FIGS. 2 to 7.

Figure 9 has a cross-sectional structure as shown in Figures 2 to 7, and
1 is an operating characteristic diagram of a superconducting multi-terminal element having a basic planar structure as shown in the figure, in which the horizontal axis shows the output current (■) and the vertical axis shows the voltage V.

The current/voltage characteristics between the superconductor electrodes 2 and 3 exhibit Josephson device characteristics as shown by the solid line in FIG.

Mode ■ is a Josephson tunneling state, and mode ■ is a Javerton tunneling state.

In the case of mode ■, a DC voltage ■7 of voltage 0 to 1■ at the residue corresponding to the barrier height between the semiconductor heavy metal or metalloid and the superconductor constituting the electrode is applied to the control electrode 7, and in the case of mode ■ is a direct current (7) of 0 to 1 mA determined depending on the size of the element, respectively, to the control electrodes 7-! When applied to the superconductor electrodes 2 and 8, the RF signal superimposed on the control electrodes 7 and 8 causes the DC characteristics to change as shown by the dotted lines in FIG. (2)23 or I23 is obtained, resulting in signal amplification, etc.

When the RF input is large, switching can be performed in a finite voltage state from zero voltage to about several mV or a finite current state from zero current to about several mA.

In this way, three-terminal characteristics can be obtained using mode 11 or the nonlinear mode (2) of the element.

In the above embodiment, the tunnel current was controlled by applying an RF signal, but the tunnel current can also be controlled by an optical signal instead of the RF signal.

That is, the optical signal may be directly introduced into the semiconductor or semi-metallic portion constituting a part of the control electrodes 7, 8 using any one of spatial propagation, optical fiber input, optical waveguide, etc.

The semiconductors used in the present invention include (Sn, Be
, Mg-doped) GaAs, InSb, Pb5nTe, C
A narrow-width semiconductor such as dHgTe or B1Sb is used, and Bi, Te or the like is used as the semimetal.

In either case, the thickness of the part in contact with the superconductor only needs to be about the coherent length of the superconductor, specifically 0.1 μm.
The following is fine.

The superconducting multi-terminal device of the present invention differs from conventional field effect transistors in that it uses superconducting electrodes as electrode pairs, that it is a quantum device that controls tunneling of electron pairs in the superconducting electrodes, and that the distance between the superconducting electrodes is It is characterized in that it is several times the coherent length or less, several hundred A or less, and that it can be used at extremely low temperatures.

As explained in detail above, the present invention is a superconducting thin film tunnel device in which a semiconductor heavy metal or semi-metal is used as a control electrode for the substance separating the superconducting electrodes, and the superconductivity of the device constituent material is improved. Since it is used at a temperature below the superconducting transition temperature of the superconducting electrode constituent material, it can be controlled by applying a minute signal to the control electrode, so it can perform analog operations such as signal detection, mixing, and amplification. It can also be applied to digital operations such as ultra-high-speed switching.

In particular, as a detection, mixing, and amplifier, it can perform coherent operation with low bias and high sensitivity in the wavelength range from submillimeter waves to optical wavelengths.

In addition, compared to conventional Josephson logic circuits, the digital operation is electric field controlled, so it is highly compatible with integrated circuits, can be expected to operate at low power, and can easily bias the nonlinear part. It has excellent advantages such as

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing the basic structure of a conventional Josephson element, FIGS. 2 to 8 are sectional views showing embodiments of the present invention, and FIG. FIG. 3 is an operational characteristic diagram of an example. In the figure, 1 is a substrate, 2 and 3 are superconducting electrodes, and 7 and 8 are control electrodes.

Claims (1)

[Claims] 1 Between at least two superconducting electrodes provided on the substrate,
A superconducting multi-terminal element comprising one or more third control electrodes made of a semiconductor thin film or a semi-metallic thin film, and controlling a tunnel current flowing between the superconducting electrodes by a control signal applied to the control electrodes.