JPH0294678A - Superconducting device - Google Patents

Abstract

PURPOSE:To make it possible to obtain a vertical laminate device by using carrier injection to modulate proximity effect in a superconducting device. CONSTITUTION:A first superconductor main electrode 12 is formed on an area of some of an insulation substrate 11 and an electrically insulated layer 13 is formed on some of the superconductor main electrode 12. The thickness of the semiconductor layer 13 is defined to be a thickness in the range in which proximity effect by virtue of superconducting is obtained. A voltage is applied between the first main electrode and a high-density impurity contained area formed on a portion of the semiconductor layer 2 and carriers are injected to a semiconductor area sandwiched by first and second superconductor main electrodes 12, 15. Since carrier density modulation in a semiconductor layer is realized by carrier injection from a control electrode in this way, a superconductor current flowing through the first and second superconductor main electrodes 12, 15 can be controlled and a vertical laminate device can be obtained.

Description

Detailed Description of the Invention [Object of the Invention] (Industrial Application Field) The present invention relates to a superconducting element using an oxide superconductor.

(Prior Art) As a superconducting element, a two-terminal superconducting element in which a pair of superconductors are opposed to each other with a tunnel insulating film interposed therebetween has been proposed and developed. However, since such conventional superconducting elements are two-terminal elements, their circuit configurations are more complex than three-terminal elements such as transistors.
The reality is that it has not yet been widely used.

For this reason, there has been a strong desire to develop a three-terminal superconducting element with an easy circuit configuration. As such a superconducting three-terminal element, a field effect element as shown in FIG. 4, for example, has been proposed.

This device has a structure in which a source electrode 2 and a drain electrode 3 each made of a superconductor are arranged close to each other on one side of a semiconductor 1, and a gate electrode 58 is provided on the back side with a gate insulating film 4 interposed therebetween. 2. The superconducting current flowing between the drain electrode 3 due to the proximity effect with the semiconductor is controlled by modulating the carrier concentration in the semiconductor by the voltage applied at the gate electrode 5 through the gate insulating film 4. ing.

In this way, in this three-terminal element, the current-voltage characteristics are made variable by applying the principle of field effect, which is well known in semiconductor devices. Although it has been experimentally shown that this device can operate, it has not yet been put into practical use due to the following problems.

In other words, this three-terminal element uses the electric field effect as its operating principle, so it is difficult to control! There is a problem in that the voltage increases and it is difficult to obtain voltage gain.

Furthermore, since the source-drain electrodes must be arranged on a plane, there is also the problem that extremely fine processing is required. Furthermore, since the size of the semiconductor region where the proximity effect can occur is narrow, about 1μ or less, it is difficult to form the gate electrode on the same surface as the main electrode. A method such as placing it on the back side of the electrode is used. Therefore, it is necessary to reduce the thickness of the semiconductor in the gate electrode portion, and there is also the problem that the processing is complicated.

(Problems to be Solved by the Invention) The present invention has been made to solve the conventional problems as described above, and modulates the magnitude of superconducting current flowing between superconducting electrodes via the proximity effect with the semiconductor. However, the present invention aims to provide a superconducting element equipped with a method for more effectively controlling the overlap of wave functions exuded from superconductors disposed in close proximity, without using the conventional principle of electric field effect. purpose.

[Structure of the Invention] (Means for Solving the Problems) A superconducting element of the present invention includes a superconductor, a semiconductor forming a junction with the first superconductor, and a semiconductor adjacent to the first superconductor. and a second bond forming a junction with the semiconductor at a position
A control terminal for injecting electrons or holes is formed in the @article conductor, and the carrier concentration in the semiconductor is modulated by the $-IJ r8 terminal to The present invention is characterized in that it is configured to control superconducting current between two superconductors.

The first and second superconductors of the present invention are not particularly limited as long as they are in a superconducting state at a given operating temperature of iJ, and metal superconductors such as Nb and Pb, Nb3Sn4, Nb3Ga4, etc. compound superconductor,
Ln-Ba-Cu-0 system (Ln is a rare earth element'), B
All known superconductors can be used, such as oxide superconductors such as 1-8r-Ca-Cu-0 series.

Further, the semiconductor used in the present invention may be any semiconductor as long as it shows good electrical contact with the first and second superconductors directly or through another conductive layer. However, in order to effectively utilize the proximity effect, a material with high mobility is desirable. Further, in order to realize carrier injection at a low operating voltage, a material with a small band gap is preferable. Note that the impurity concentration of the semiconductor interposed between the superconductors does not need to be constant. For example, a portion close to the superconductor electrode may contain a high concentration of impurity to improve electrical contact, and a portion away from the superconductor electrode may contain a relatively low concentration of impurity.

In the superconducting element of the present invention, the voltage application for carrier injection into the semiconductor is based on the high concentration impurity region formed in a part of the semiconductor layer and the difference in the impurity content of the semiconductor layer between the two superconductors. Since the built-in voltage can be set to a small value, it can be set to a significantly smaller value than when using an electric field effect.

(Function) Generally, when a junction is formed between a superconductor and a semiconductor, the wave function of the superconducting state oozes out from the superconductor to the semiconductor, so that the semiconductor itself in a region close to the superconductor begins to exhibit superconducting characteristics.

This phenomenon is called the proximity effect,
The size of a semiconductor region exhibiting a superconducting state is a function of carrier concentration and mobility in the semiconductor. Therefore, if two superconductor electrodes are arranged with a semiconductor layer in between and the carrier concentration in the semiconductor phase is modulated, the wave functions seeping out from the two superconductor electrodes will overlap, creating a state in which superconducting current flows. , the overlap of the wave functions can realize a three-terminal element that switches 17i1 to a state in which no superconductor current can flow.

The present invention is configured to realize carrier concentration modulation in the semiconductor layer by carrier injection from a control electrode.

That is, a region containing a high concentration of impurities is formed in at least a part of the semiconductor layer including the region where the first and second superconductors are joined, a control electrode is provided on this region, and a voltage is applied to the control electrode. is applied to inject carriers into the semiconductor region between the two superconductors by diffusion. The applied voltage necessary for carrier injection can be set to a sufficiently small value because it is about the built-in voltage caused by the difference between the impurity concentration in the region where the control electrode is formed and the impurity concentration contained in the semiconductor region between the superconductors. It is possible.

According to the present invention, as will be shown in later examples, it is possible to obtain a vertical multilayer element that could not be realized using the conventional principle of field effect.

Generally, the size of the semiconductor region where the proximity effect can occur is 0.
In the case of horizontal elements in which the main electrodes are formed on the same plane, significant microfabrication is required because the color is narrower than 1 μm μm.
With this vertical configuration, ultra-fine processing can be avoided.

Further, even in the case of a horizontal element, since the control electrode can be formed on the same surface, there is no need to make the semiconductor in the control electrode portion thinner, and there is an advantage that processing is easy.

(Example) Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is an enlarged sectional view of a vertical superconductor three-terminal element according to an embodiment of the present invention.

In the embodiment shown in FIG. 1, a first superconductor main electrode 12 is formed on a part of an area on an insulating substrate 11, and an electrical insulating layer 13 is formed on a part of this superconductor main electrode 12. ing. Further, a semiconductor layer 14 is formed from the insulating substrate 11 to the superconductor main electrode 12 and the electrically insulating layer 13, and "n+" is diffused by phosphorus into the portion of the semiconductor layer 14 located on the electrically insulating layer 13. There is. Note that the thickness of this semiconductor layer 13 is within a range where the proximity effect due to superconductivity can be obtained. Furthermore, the substrate 11 of the semiconductor layer 14
A second superconductor main electrode 15 is formed on a portion formed from the first superconductor main electrode 12 to the first superconductor main electrode 12 .

and first and second superconductor main electrodes 12.15,
Each of the high concentration impurity containing regions 14a formed in a part of the semiconductor layer 14 is provided with an electrode terminal.

In this element, a voltage is applied between the first main electrode 12 and a high concentration impurity containing region 14a formed in a part of the semiconductor layer 2, and the region is sandwiched between the first and second superconductor main electrodes 12.15. By injecting carriers into the semiconductor region, the superconductor current flowing between the first and second main electrodes 12.15 can be controlled.

In order to actually create an element with such a structure, it is desirable to form a laminated structure epitaxially. For this purpose, in terms of material, for example, A2
□03 Single crystal, first and second superconductor main electrodes 12.15
A combination of Nb as the material and Ge as the semiconductor layer 14 is suitable.

FIG. 2 shows the current-voltage characteristics between the first and second superconductor main electrodes 12, 15 of the embodiment shown in FIG. 1 using the control electrode voltage vG as a parameter.

It can be seen from this graph that the main electrode current is controlled by changing the control electrode voltage.

FIG. 3 schematically shows a superconductor transistor according to another embodiment of the present invention, and shows the case of a horizontal element in which the main electrode is formed on the surface of a semiconductor substrate. In this embodiment, two main electrodes 21 and 22 made of a superconductor are formed on one surface of a semiconductor substrate 23 with a distance of about 0.1 μm, and a control electrode 24 for carrier injection is formed between the two main electrodes 21 and 22. High concentration impurity containing region 2 located close to the electrode
3a. According to this embodiment, the main electrode 2
1.22 Although ultrafine processing is required for formation, the main electrode and the injection electrode can be formed on the same surface, and the selection of the semiconductor material and superconductor material can be made more freely than in the first embodiment. There is an advantage that it can be done.

[Effects of the Invention] As described above, according to the present invention, by utilizing the new concept of using carrier injection to modulate the proximity effect in a superconducting device, it is possible to create a vertical box layer device that could not be realized in the past. Furthermore, even in the case of a horizontal element, the control electrodes can be formed on the same surface, so there is no need to make the semiconductor in the control electrode portion thinner, and there is an advantage that processing is easy.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view showing a superconducting three-terminal element with a vertical configuration according to an embodiment of the present invention, FIG. 2 is a diagram showing its current-voltage characteristics, and FIG. FIG. 4 is a perspective view showing a three-terminal device, and FIG. 4 is a diagram showing a conventional field effect transistor. 11...Insulating substrate 12...First superconductor main electrode 13...
..... Electrical insulating layer 14 ..... Semiconductor layer 15 ..... Second superconductor main electrode 21.2
2... Main electrode 23... Semiconductor substrate 24... Control electrode

Claims (1)

[Claims] (1) A first superconductor, a semiconductor forming a junction with the first superconductor, and a second superconductor forming a junction with the semiconductor at a position close to the first superconductor. A control terminal for injecting electrons or holes is formed in the semiconductor, and the control terminal controls a superconducting current between the first and second superconductors by modulating the carrier concentration in the semiconductor. A superconducting element characterized by being configured to.