JPS6257260A - Superconducting transistor - Google Patents

Abstract

PURPOSE:To improve the uniformity of the characteristics, the reproducibility and the gain of the device by providing first and second superconducting electrodes above and below the semiconductor, and providing an insulating film and a control electrode on the end portion thereof, thereby enhancing the process precision. CONSTITUTION:First and second superconducting electrodes 1, 2 are stacked above and below a semiconductor 3, and on the side wall portion thereon a third control electrode 4 isolated by an insulating film 5 is disposed. For instance, a 300nm thick Nb thin film 2 is deposited on substrate 8 by means of the DC magnetron sputtering method, on the surface of which a channel layer 3 of 200nm thick Si is immediately formed by means of the vapor growth or molecular beam growth method, and impurity B is introduced by means of the ion drive-in method. Again, a 300nm thick Nb thin film 1 is deposited, forming a lamination structure. After processing this into a desired shape by means of the ion etching method, the surface of the side wall portion is thermally oxidized, obtaining an insulating material 5. Finally, after depositing Nb by means of the DC magnetron sputtering method, this is processed by means of the reactive ion etching by CF4 gas, obtaining the control electrode 4.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a superconducting device that operates at extremely low temperatures, and particularly to a superconducting device in which the number of superconducting electrons tunneling through a semiconductor is controlled by a voltage applied to a control voltage.

[Background of the invention]

A conventional superconducting device combining a superconductor and a semiconductor has a structure shown in FIG. 1, as described in Japanese Patent Laid-Open No. 57-016186.

This is a tIII structure in which a control electrode 4 is provided between a pair of superconducting electrodes 1 and 2 facing each other.

In order for the two superconductors of this disk to achieve a superconducting weak coupling state through the semiconductor at extremely low temperatures, the distance between the two superconductors must be 10 times the coherence length of the electron pairs in the superconductors.
It is necessary to approach the distance by about twice as much, that is, by 0.2 μm or less. In this prior art, two superconducting electrodes are first formed integrally and then separated into two superconducting electrodes 1 and 2 by photolithography and etching. Subsequently, the separated portion is thermally oxidized to form a reinforcing film 5, and the control electrode 4 is installed by vapor deposition. According to this method, since the distance between the superconducting electrodes 1 and 2 is as narrow as 0.2 μm or less, it is difficult to form the insulator 5 and the control electrode 4 in this area. Further, even if it could be formed, there was a drawback that the dimensional accuracy of processing could not be improved.

[Purpose of the invention]

The purpose of the present invention is to improve the processing accuracy of a superconducting transistor that combines a semiconductor and a superconductor and operates at extremely low temperatures, thereby improving the uniformity, reproducibility, and gain of device characteristics. The purpose of this invention is to provide a structure and manufacturing method for a superconducting transistor that can be manufactured.

[Summary of the invention]

In order to achieve this object, the present invention has first and second superconducting electrodes installed above and below a semiconductor, and a third gate electrode separated from the semiconductor by an insulating film. The superconducting weak coupling state of the electrodes is controlled by the voltage applied to the third electrode. At the point where the superconductor and semiconductor are in contact, the order parameters of the superconductor leak into the semiconductor, and the spatial distance is the coherence length ξ of the electron pairs in the semiconductor. is expressed by

When the spatial distance between the first and second superconducting electrodes is 10 times or less the coherent length, a weakly coupled superconducting state can be achieved. In the case of the superconducting transistor of the present invention, the distance (2) is determined by the thickness of the semiconductor between the superconductors. On the other hand, the value of ξ changes depending on the temperature T, the carrier concentration N in the semiconductor, and the type of semiconductor and superconductor, and the larger N is, the larger ξ is. also becomes larger. Therefore, the larger the value of the ratio of ξ and ■, which is 0.7, the stronger the coupling between the superconductors. Therefore, by applying an electric charge to the control electrode, electric charge can be accumulated and controlled in the semiconductor.

Here, the value of I, when the transistor is ON, is ■, /ξ,
The design must be such that the ratio is 10 or less. When an Sj semiconductor is used for the channel, it is desirable that the value of (1) be selected in the range of 0.1 to 0.2 μm.

In the superconducting transistor of the present invention, since the value of D is determined by the thickness of the semiconductor, it is easy to control uniformity, and the reproducibility and uniformity of transistor characteristics during manufacture are extremely excellent. Further, by using superconducting transistors with this structure, a composite device can be constructed by connecting a plurality of transistors in series to increase the output amplitude.

[Embodiments of the invention]

Hereinafter, the present invention will be explained in detail using Examples.

FIG. 2 is a sectional view of a superconducting transistor according to a first embodiment of the present invention. First and second superconducting electrodes 1. above and below the semiconductor 3. ．． A third control electrode 4 is provided on the side wall of the control electrode 2, which is separated by an insulating film 5.

A field effect transistor is configured in which a superconducting weak coupling state between the first and second electrodes is controlled by a voltage applied to the third electrode. If the superconducting weak coupling state can be controlled, the flowing superconducting current can be changed.

Next, a method of manufacturing this superconducting transistor will be explained (FIG. 3). Immediately on the surface of the Nb thin film 2 with a thickness of 300'nm deposited on the substrate 8 by the DC magnetron sputtering method, a channel layer 3 made of Si with a thickness of 200nm is formed by vapor phase epitaxy or molecular beam epitaxy. Then, impurity B is added to 1025 by ion implantation method.
(2)-3 was introduced. Again 300 nm thick Nb@film 1
is deposited to form a laminated structure. This was processed into a desired shape by an ion etching method using photonodist as a mask (5), and then the surface of the side wall portion was thermally oxidized for 10 minutes in an oxygen atmosphere at 1000° C. to obtain an insulator 5 with a thickness of about 20 nm. Finally, Nb was deposited to a thickness of about 800 nm by DC magnetron sputtering. After that, this was processed by reactive ion etching using CF4 gas to form a 2 μm wide N film on the right side of the thermal oxide film.
The third electrode 4 is obtained by leaving b. Through the above steps, the superconducting transistor of this example shown in FIG. 2 could be manufactured.

According to this embodiment, since the thickness of the semiconductor is used to determine the distance between the superconducting electrodes, it can be controlled accurately, suppressing variations in transistor characteristics, and improving yield during manufacturing. I can do it. Further, since an interlayer insulating film is not required, the manufacturing process becomes easier.

FIG. 4 is a sectional view of a superconducting transistor according to an embodiment of the tube 2 of the present invention. It has a structure in which two transistors are connected in series to one control electrode 4 using a superconducting electrode 2 in common. Figure 6 shows the fabrication of this device]
; indicates the degree.

As shown in the first embodiment (Nb thin film 2. Si semiconductor 3
and Nb thin film 1 are laminated (FIG. 6(a)).

Thereafter, the Nb thin film 1. Separate the semiconductor 3 into two. After that, the surface of this groove is thermally oxidized to form an insulator 5.
(Fig. 6(b)), on which Nb with a thickness of 500 nm was deposited and the control electrode 4 was installed (Fig. 6(C)).
.

The superconducting transistor of this example shown in FIG. 4 could be manufactured by the following steps. According to this embodiment, two superconducting transistors can be easily connected in series, so
The output amplitude for a constant control voltage can be doubled, and the circuit gain can be increased. Further, the terminals of the electrodes can be taken out from the same side. On the other hand, since the superconducting electrode and channel layer can be formed at once without doubling the number of manufacturing steps, there are advantages such as ease of high integration.

FIG. 5 is a sectional view of a superconducting transistor according to a third embodiment of the present invention. A plurality of superconducting transistors according to the second embodiment are further connected, holes are formed between the elements by chemical etching with a KOH solution, and Si is deposited on the holes by vapor deposition.
A separation layer 6 was formed by burying O. According to this embodiment,
The output amplitude for a constant input applied to the control electrode 4 can be increased, and the circuit gain can be increased. Also made,
It has the advantage of being easy to increase the volume.

In the three embodiments shown below, the first. 2nd゜3rd
Nb was used as the electrode material, but NbN.

Nb compounds such as Nb3Ge, Nb3Sn, NbaAI2, or Pb-Au, Pb-In-An.

Similar effects can be obtained even when a pb gold alloy such as Pb-B1 is used. In addition, the material of the third electrode includes AQ,
The object of the present invention could be achieved even by using polycrystalline Si or single crystalline Si containing impurities at a high concentration.

In addition to Si and tit crystals, polycrystalline Sj
.

Amorphous Si, Ge, InAs of GaAs
, I n P .

TnSb or the like may also be used.

In addition, the materials of the insulating film 5 include SiO, Si, N4
A similar effect could be obtained using . Note that the impurity concentration of the semiconductor is 10" in order to operate at extremely low temperatures.
It is desirable that the value is m-' or more.

The impurity is selected from P, R, AS, Sb, etc.

[Effects of the Invention] According to the present invention, a superconducting transistor that can be controlled by voltage can be realized and manufactured with good reproducibility and uniformity. Furthermore, since the superconducting transistor of the present invention can be easily connected in series and its minute dimensions can be controlled, it has the effect of realizing a high-speed, highly integrated superconducting integrated circuit.

[Brief explanation of drawings]

Figure 1 is a sectional view showing a conventional superconducting transistor, Figure 2 is a cross-sectional view showing a conventional superconducting transistor.
3 is a sectional view of a superconducting transistor according to an embodiment of the tube 1 of the present invention, FIG. 4 is a sectional view of a superconducting transistor according to a second embodiment, and FIG. 5 is a sectional view of a superconducting transistor according to a third embodiment. Cross-sectional views, Figures 6 (a) to (c) are the second
FIG. 3 is a cross-sectional view showing the manufacturing process of a superconducting transistor according to an embodiment of the present invention. 1.2... Superconducting electrode, 3... Semiconductor, 4... Control electrode, 5... Insulating film, 6, 7... Insulating layer, 8...
·substrate.

Claims (1)

[Claims] 1. It has a structure in which an electrode made of a first superconductor, an electrode made of a semiconductor, and a second superconductor are stacked, and an insulating film and a control electrode are provided at the ends thereof. superconducting transistor. 2. A superconducting transistor according to claim 1, wherein the thickness of the semiconductor is selected to be in the range of 0.1 to 0.2 μm.