JPH01205578A - Superconductive field effect transistor - Google Patents

Abstract

PURPOSE:To obtain a superconductive field effect transistor easy to be made and able to control a big current by providing a superconductive layer to be realized by excess or scarcity of electrons to be caused near a junction interface of two kinds of materials having different electron affinity and an electrode impressing an electric field extinguishing excess or scarcity of electrons. CONSTITUTION:A BaPb1-xBixO3 layer 2, BaPb1-yBiyO3-delta layer 3 (0.35<x<y) is formed on an SrTiO3 single-crystal substrate 1. A material of the layer 2 becomes a superconductor having a critical temperature of about 13K in the case of x<0.35, while becoming a semiconductor or an insulator in the case of x>0.35, and even in the case of x>0.35, a superconductive layer 4 is generated due to excess or scarcity of electrons caused near a junction interface of the layers 1 and 2. Excess or scarcity of electrons near the interface can be extinguished by voltage to be impressed on a C electrode 6 enabling a superconductive current flowing between an A electrode 5a and a B electrode 5b to be controlled.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to superconducting transistors, and particularly to superconducting field effect transistors in which superconducting current can be controlled by an externally applied electric field.

[Conventional technology]

Figure 5 is an example of applied physics Vol. 1.56 pya 6 (19
87) P, '753 This shows the conventional superconducting transistor reported by Nishino et al. In the figure, (7) is a silicon single crystal, (8a) and (8b) are one with the A electrode,
The other is a superconducting electrode (lead alloy) which is a B electrode, and (9) is a gate electrode (Al) which is a 0 electrode. σO is a gate insulating film (sio2).

Next, we will explain the operation. In general, in a thread where a superconductor and a normal conductor are in contact, the coherence length of the normal conductor (or semiconductor) is approximately the same as the coherence length of the normal conductor (or semiconductor). It is possible to seep into the range of .

This coherence length depends on the carrier concentration 0 Now, A'fl! , by applying a voltage between the pole and the gate electrode (9), the silicon single crystal (7) near the gate electrode (9)
Increasing the carrier concentration within increases the coherence length. At this time, if you try to flow a current between the A and B electrodes, if the distance between the A2B electrodes is about the coherence length, the Cooper pair of electrons that entered the silicon single crystal (7) from the A electrode will reach the B electrode. Current flows. On the other hand, if no voltage is applied to the gate electrode, the number of carriers decreases and the coherence length becomes short, so that no current flows between the A and B electrodes. By changing the gate voltage in this manner, the superconducting current flowing between the A and B electrodes is controlled.

[Invention or problem to be solved]

Conventional superconducting transistors use the current generated by Cooper's pair of electrons seeping into the semiconductor, so it is difficult to obtain a large superconducting current. In addition, processing is difficult because it is necessary to make the electric current tM [41 total coherence length (approximately 0.2 μm or less) long. Furthermore, since the gate mill quadrupole part needs to be placed close to the A and B electrodes, it is necessary to thin the Si crystal to a thickness of about 0.1 μm, which also makes manufacturing difficult.

The present invention was made in order to solve this problem, and an object of the present invention is to obtain a superconducting field effect transistor that is easy to manufacture and can control a relatively large superconducting current.

[Failure to solve the problem]

The superconducting field effect transistor according to the present invention exhibits insulating or semiconducting properties, metallic properties, and superconducting properties depending on the composition ratio, temperature, and amount of defects. Material systems that exhibit insulating or semiconducting properties and differ in electron affinity or ionization energy2
A superconducting layer is realized by inducing an excess or deficiency of electrons near the bonding interface between the two materials by bonding two different materials, and a first layer is provided at both ends of this superconducting layer to conduct a superconducting current.
and a third electrode which is provided to sandwich the above-mentioned material exhibiting insulating or semiconducting properties between the second electrode and the superconducting layer, and applies an electric field to annihilate the superconducting layer. It is prepared.

[Effect]

In this invention, superconducting current is interrupted by applying an external electric field to eliminate excess or insufficient electrons in the superconducting layer.

[Embodiments of the invention]

FIG. 1 is a sectional view showing a superconducting field effect transistor according to an embodiment of the present invention, and (1) is a sectional view showing a superconducting field effect transistor according to an embodiment of the present invention.
Single crystal of rTi○5, (2) is EaPbl-xBlx03 prepared using a magnetoconverter etc. on the substrate.
In the first layer, the value of X is about 035 or more, for example 04.
It is the material. (3) is a BaPb1-yBiy03-δ layer made by changing the sputtering conditions;
For example, the second material is set to y-08 so that the value of is larger than X, and δ takes a value other than O. These two types of lateral slopes (13a'PbBiO3J) exhibit insulating or semiconducting properties. Physical properties of this material and 2 above
The fact that a superconducting layer is induced when seed materials are joined is that
For example, a patent application filed by the same applicant in 1982-
Since it is described in detail in No. 281624 "Superconductor Device", it will be explained here by quoting it.

First, BaPb1 and Bix03 have insulating or semiconducting properties, metallic properties, and superconducting properties depending on the composition ratio and temperature, as shown in Figure 2 - Phase diagram of their electronic properties. It is also known that the above-mentioned properties can be exhibited depending on the amount of defects. In other words, x (035 is a superconductor with a critical temperature of about 13, but as X becomes thicker in the region of However, a gap is created between the two, and as the free carriers disappear, the energy of the upper empty band increases and the electron affinity decreases.Thus, the insulator still exhibits semiconducting properties, but this It is believed that superconductivity can occur if there are sufficient free carriers in the region.

Next, the induction of a superconducting layer by bonding will be explained.

FIG. 3 is a band diagram of a conduction band corresponding to the structure shown in FIG. 1, in which the horizontal axis represents the distance 11 in the film thickness direction, and the vertical axis represents the electron energy E.

A is the region of BaPb1-XBlx03 (x>0.35), B is the region of B L Pb 1- yE i yO5-δ
The region of (y>X, δ knee, o) is shown. 0]] is A, 1
3 represents the junction interface, OΔ represents the conduction band, and σ3 represents the electrons accumulated at the interface. EF is Fermi energy. Now, if free electrons are introduced to the B side, that is, to the side with a smaller electron affinity, they can be made to flow to the A side, which has a much larger electron affinity. A possible method for introducing free electrons is to introduce oxygen vacancies. When the oxygen content of BaPb1 yBiy03, which has become a semiconductor, is reduced from the stoichiometric value of 3 to 3-δ, a level due to oxygen vacancies is generated, and free electrons appear in the conduction band. . These electrons flow more strongly to the A side of the electron affinity. Due to the bending of the band caused by the attractive force between the positive charges left behind by the flowing electrons and the flowing electrons, electrons accumulate at a high concentration near the interface.

When the frequency of the band is large and the field is around 1 m or below the Fermi energy EF, an electron gas state is created there. When the concentration of two-dimensional electron gas generated near such an interface reaches a certain level, a superconducting state can be achieved at low temperatures.

A superconducting state can also be obtained by making use of the difference in ionization energy between the two materials to be bonded to create a layer with an excess of holes, that is, a layer lacking electrons, near the bonding interface. The band diagram of the valence band in this case is shown in FIG.

In the figure, the horizontal axis represents distance in the film thickness direction, and the vertical axis represents electron energy. A is a material with a smaller ionization energy,
B represents a material with higher ionization energy. The circle represents the junction interface of A and E, the valence band and the holes accumulated at the interface.

EF Hafelmi energy. In this case, Schiffly holes are generated on the B side by doping or introducing defects. Then, due to the difference in ionization energy, this hole moves to the side of A, and as shown above, a hole gas is created this time. This part then becomes superconducting.

This electron gas or hole gas was originally induced by the band's songs. Therefore, the thickness of the electron gas or hole gas can be controlled by applying an external electric field that changes the band curvature. For example, by applying a sufficiently large electric field, the electron gas or hole gas can be eliminated, and superconducting states can no longer exist.

In this way, a superconducting layer can be realized by joining two materials that exhibit insulating or semiconducting properties and have different electron affinities or ionization energies, and this superconducting state can be achieved by applying an external electric field. It can be controlled by The first application of this was as a field effect transistor.
1 is an embodiment of the invention shown in the figure; In the figure, (4)
is a superconducting layer induced by joining the above two materials, (
5a) + (5b) are electrodes that are provided at both ends of this superconducting layer and allow superconducting current to flow, one of which is the first electrode (octupole).
, the other is the second electrode (B electrode). (6) is provided to sandwich a material (layer) exhibiting insulating or semiconducting properties with a superconducting layer, and is used to apply an electric field to extinguish excess or insufficient electrons in the superconducting layer from the outside. 'electrode(
C electrode).

In a superconducting field effect transistor configured in this way, when a suitable electric field is applied to the 0 electrode while a superconducting current is flowing through the superconducting layer between the A and B electrodes, the superconductor near this electrode is The band near the layer is deformed, and the electron gas or hole gas mentioned above increases, making it impossible for the superconducting layer to exist in this vicinity. Therefore, superconducting current no longer flows.

In this way, a superconducting current can be caused to flow or be interrupted by an electric field applied from an electrode. In the above embodiment, two types of junctions exhibit insulating or semiconducting properties and have different electron affinities or ionization energies. Although BaPbB105 is shown as a material that can be bonded, it is possible to create a superconducting layer by inducing an excess or deficiency of electrons near the bonding interface, and it is possible that this is a material that can be controlled by an external electric field. produces the same effect as the above embodiment.

Furthermore, if the width of the C electrode to which the electric field is applied is narrowed, the area where the superconducting layer cannot exist will become narrower.

Therefore, a weakly coupled state of the superconducting layer exists depending on the applied electric field, and a Josephson coupled field effect transistor can be obtained in which the weakly coupled region can be controlled depending on the magnitude of the electric field.

〔Effect of the invention〕

As described above, according to the present invention, depending on the composition ratio, temperature, and amount of defects, the properties of an insulator or a semiconductor,
By joining two materials that have insulating or semiconducting properties and have different electron affinities or ionization energies in a material system that exhibits metallic properties and superconducting properties, υ A superconducting layer realized by inducing an excess or shortage of electrons near the bonding interface of both materials, first and second electrodes provided at both ends of this superconducting layer to flow a superconducting current, and the above insulator or The third electrode is placed between the side slope exhibiting semiconducting properties and the superconducting layer, and applies an electric field to annihilate excess or insufficient electrons in the superconducting layer, making it easy to manufacture and easy to compare. Superconducting field effect transistors that can control large superconducting currents have the advantage of

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view showing a superconducting field effect transistor according to an embodiment of the present invention, FIG. 2 is a phase diagram showing electronic properties of BaPb1-xBixo 3 used in the embodiment of FIG. 1, and FIG. FIG. 4 is a characteristic diagram showing a conduction band or valence band diaphragm corresponding to the structure shown in FIG. 1, and FIG. 5 is a cross-sectional view showing a conventional superconducting transistor. In the figure, (2) is the first material (BaPb1-xBix
o3 layer), (3) is the second material (Barb 1-yBi3
r03-δ layer), (4) is a superconducting layer, (5a), (5b
) is the first electrode (A electrode) and the second electrode (B electrode),
(6) is the third electrode (0 electrode). Note that the same reference numerals in each figure indicate the same or corresponding parts.

Claims (1)

[Claims] An insulator or semiconductor is a material system that exhibits insulator or semiconductor properties, metallic properties, and superconductor properties depending on the composition ratio, temperature, and amount of defects. A second material, which is in the above-mentioned material system and exhibits insulating or semiconducting properties and has a different electron affinity or ionization energy from the first material, is added to the first material that exhibits the properties of
A superconducting layer that is realized by bonding materials and inducing excess or deficiency of electrons near the bonding interface of both materials, and first and second electrodes that are provided at both ends of this superconducting layer and allow a superconducting current to flow. , a third electrode that is provided so as to sandwich the first material or the second material with the superconducting layer and applies an electric field to annihilate excess or insufficient electrons in the superconducting layer. field effect transistor.