JPS61206277A - Superconductive transistor - Google Patents

Abstract

PURPOSE:To improve the accuracy of finishing of a superconductor while enhancing the reliability and uniformity of element characteristics by forming a projecting section consisting of a semiconductor onto a substrate and shaping a pair of superconductive electrodes brought into contact with both sides of the projecting section and a control electrode to the upper section of the projecting section through an insulator layer. CONSTITUTION:An Si single crystal substrate 1 is oxidized to shape an insulator layer 6 on the surface of the substrate, a control electrode 5 consisting of polycrystalline Si is formed through electron0beam evaporation, and the layer 6, the electrode 5 and one part of the substrate 1 are etched through plasma etching while using an electron-beam resist as a mask. Superconducting electrodes 2, 3 are shaped, and the side surface of the control electrode 5 is thermoset to form an insulator layer 7. Accordingly, a projecting section 4 as a channel layer can be shaped easily with high precision while a distance between superconductors can be determined with high accuracy, thus acquiring a switching element having high reliability.

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 combination of a semiconductor and a superconductor.

The present invention relates to a field-effect superconducting transistor having a control electrode.

[Background of the invention]

A superconducting device that combines a semiconductor and two superconductors is an example of using a degenerate Si single crystal as a semiconductor.
“,
Alternatively, Example 4 is known in which p-type GaAs is used as the semiconductor. In these examples, PB is used as the superconductor, and an etching method using a photoresist as a mask is used for processing. In order for the two superconductors of this device to form a superconducting weak coupling via the semiconductor at extremely low temperatures, the distance between the two superconducting electrodes must be approximately 10 times the coherent length of the electron pairs in the superconductor, or approximately 0. It is necessary to bring the distance closer to .5 μm or less. FIG. 1 shows the structure of a conventional superconducting transistor disclosed in Japanese Patent Application Laid-Open No. 57-106186. In this structure, first, two superconducting electrodes 2 and 3 are formed integrally,
Next, etching is performed using photoresist or electron beam resist as a mask to form two superconducting electrodes 2 and 3 that are close to each other.

Subsequently, a thermal oxide film 6 of about 80 nm is formed, and then a control electrode 5 is formed between the superconducting electrodes 2 and 3. However, in the conventional structure shown in Figure 1, 0.5 μ
It is not easy to form a control electrode in a narrow space of less than m, and for this reason, the dimensional accuracy of processing is not high.
It was difficult to obtain reliability and uniformity.

[Purpose of the invention]

An object of the present invention is to provide a superconducting transistor in which the processing accuracy of the superconductor is improved and the reliability and uniformity of the device characteristics are improved in a transistor-type element that combines a semiconductor and a superconductor and operates at extremely low temperatures. It is in.

[Summary of the invention]

In order to achieve the above object, the present invention forms protrusions by etching on the semiconductor substrate side, in place of conventional etched superconducting electrodes, and provides control electrodes on these protrusions via an insulating layer. It is characterized by the fact that According to this structure, the spatial distance between the two superconductors is determined by the processing precision of the semiconductor substrate. Therefore, it is possible to improve the uniformity of device characteristics and increase the yield during manufacturing. Furthermore, by insulating the side surfaces of the control electrode, the control electrode and the superconducting electrode are completely insulated, making it possible to further improve the uniformity and reliability of device characteristics.

[Embodiments of the invention]

An embodiment of the present invention will be described below with reference to FIGS. 2 and 3.

FIG. 2 is a cross-sectional view of the superconducting transistor structure of the present invention. A portion of a semiconductor substrate 1 has a protrusion 4, and a pair of superconducting electrodes 2 and 3 facing each other are formed on both sides of the protrusion. A control electrode 5 whose side surfaces are insulated is provided on the protrusion 4 with an insulator layer 6 interposed therebetween.

The manufacturing process of this device will be explained with reference to FIG. Si
A single crystal substrate 1 is oxidized with oxygen containing water vapor at 1200° C. for 1 hour to form an 80 nm thick insulating layer 6 made of Sin on the substrate surface. Next, a control electrode 5 made of polycrystalline Si with a thickness of 0.3 μm is formed by electron beam evaporation in a high vacuum container, and then a part of the substrate 1 is etched by plasma etching with CF4 gas using the electron beam resist as a mask. do. Next, a superconducting electrode 2.3 with a thickness of 300 nm made of pb
was formed using a resistance heating evaporation method and a lift-off method, and then the side surface of the control electrode 5 was thermally oxidized to form an insulating layer 5.

In addition to Sin, the material of the insulator layers 6 and 7 is Si
It can be selected from among O, Si, N, AM, O, etc. Semiconductor materials include P and B.

Si or Ge containing impurities such as As at 10"a++-' or more, or Si, Zn containing 10"cm-" or more
.

GaAs, InAs, I containing Ge as an impurity
nP or the like may also be used as the material for the control electrode 4.

T i, W, Mo, Po1y-5i+ AQ,
Cu, P, etc. may also be used.

As the material for the superconducting electrodes 2 and 3, pb, an alloy containing pb as a main component, Nb, a Nb compound, etc. may be used.

In the superconducting transistor manufactured in this way, the protrusion 4 which becomes the channel layer can be easily and accurately formed to a thickness of 0.5 μm or less, which is about 10 times the coherent length of the superconductor.

In other words, since the spatial distance between the superconducting electrodes was formed with high precision, it was possible to obtain a device with small variations in characteristics and high yield.

Furthermore, although the operating principle is that the superconducting weak coupling state between the two superconducting electrodes 2 and 3 changes depending on the voltage applied to the control electrode 4, an insulator layer 7 is formed around the control electrode 4 to By separating the two, malfunctions can be prevented.

Furthermore, since the superconducting electrodes 2 and 3 are facing each other, current flows easily between them, and a higher speed superconducting transistor can be obtained.

Furthermore, since a self-lay process can be applied, the number of mask steps is also reduced, making the process easier.

FIG. 4 shows another embodiment of the invention. This embodiment has a structure in which a plurality of source and drain electrodes are connected in series to one control electrode. That is, three protrusions 4 formed by the method described in the previous embodiment are provided on the substrate 1, and superconducting electrodes 9, 10, 11, and 12 are provided to sandwich these protrusions, respectively. ing. One control electrode 13 is provided on the three protruding portions with an insulating layer 6 interposed therebetween. The inner superconducting electrodes 10 and 11 have two roles: the left end serves as a natrain, and the right end serves as a source. According to this element, an output voltage three times the output voltage of one superconducting transistor can be obtained. That is, by increasing the number of superconducting electrodes connected in series to one control electrode, it is possible to increase the circuit gain.

〔Effect of the invention〕

According to the present invention, in a superconducting transistor in which two superconductors are coupled via a semiconductor, the distance between the superconductors is determined with high accuracy, so variations in transistor characteristics can be suppressed, and therefore, reliable high-speed This has the effect of providing a switching element.

[Brief explanation of drawings]

Fig. 1 is a cross-sectional view of a conventional superconducting transistor, Fig. 2 is a cross-sectional view of a superconducting transistor according to an embodiment of the present invention, Fig. 3 is a diagram of its manufacturing process, and Fig. 4 is a superconducting transistor according to another embodiment of the present invention. FIG. 2 is a cross-sectional view of a transistor.

Claims (1)

[Claims] 1. A substrate having a protruding portion made of a semiconductor; a pair of superconducting electrodes formed on the substrate and provided in contact with both sides of the protruding portion; A superconducting transistor characterized by having a control electrode provided through an insulating layer. 2. The superconducting transistor according to claim 1, wherein the control electrode has an insulated side surface. 3. A superconducting transistor according to claim 1 or 2, wherein the control electrode is made of polysilicon. 4. A superconducting transistor according to claim 1 or 2, wherein the control electrode is made of a normal conducting metal.