JPS61239681A - Superconducting element - Google Patents

Abstract

PURPOSE:To increase the switching rate of an element by forming an electrode consisting of a superconductor onto a substrate through an insulating film, shaping a semiconductor layer onto the electrode and forming a control electrode onto the semiconductor layer through an insulator layer. CONSTITUTION:An insulating film 2 is shaped onto an Si substrate 1, and an electrode 3 composed of a superconductor is formed onto the insulating film 2. A semiconductor layer 4 is shaped onto the electrode 3. The shape of the layer 4 is determined so that the layer 4 extends over the upper sections of both the film 2 and the electrode 3 including regions except a region 5 to which the electrode 3 faces. An insulator layer 6 is formed onto the surface of the layer 4, and a control electrode 7 consisting of a metal or a semiconductor is shaped onto the layer 6. Consequently, when shaping a superconducting element, substrate capacitance is not formed because the semiconductor layer through which superconductive currents or normal conductive currents flow is insulated electrically from the substrate. Accordingly, a switching rate in circuit operation can be increased.

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 that is formed by combining a superconductor and a semiconductor.

[Background of the invention]

Conventionally, there is a superconducting element that combines a superconductor and a semiconductor described in Japanese Patent Laid-Open No. 106186/1986. This superconducting element is constructed by depositing a pair of superconducting layers on a semiconductor substrate with their end surfaces facing each other, and disposing a control conductor on the opposing portions with an insulating layer interposed therebetween.

That is, although the control conductor controls the current flowing between the superconductor layer, the semiconductor substrate, and the superconductor layer, it is not possible to increase the switching speed in circuit operation due to the substrate capacitance of the semiconductor.

[Purpose of the invention]

An object of the present invention is to provide a superconducting element that can increase the switching speed of the element.

[Summary of the invention]

In order to achieve the above object, the present invention forms an electrode made of a superconductor on a substrate that becomes an insulator at least at extremely low temperatures or an insulating film formed on the substrate, and forms a semiconductor layer on the electrode. Furthermore, a superconducting element is constructed by forming an insulating layer on this semiconductor layer and forming a control electrode on the insulating layer.

In this way, the semiconductor layer through which superconducting current or normal conducting current flows is electrically insulated from the substrate and therefore does not have so-called substrate capacitance. Therefore, it is possible to increase the switching speed in circuit operation. Furthermore, since a high-resistance material can be used as the substrate material, when a large number of superconducting elements are formed on the substrate, it can be used without providing special isolation between elements within the substrate.

Furthermore, it is effective to perform heat treatment to improve the crystallization and electrical properties of the semiconductor layer. In this case, the superconducting properties of the superconductor under the semiconductor layer may deteriorate. According to the studies conducted by the present inventors, NbN, Nb
3Si, Nb, Ge.

It has been found that when M o N, V3S i is used, the characteristics of the superconductor under the semiconductor layer do not deteriorate even if the semiconductor layer is subjected to heat treatment. This makes it possible to heat-treat the semiconductor layer, for example to increase the crystal grain size of the semiconductor or to recrystallize it, making it possible to form a single crystal mainly in the (100) plane, thereby improving the characteristics of the superconducting element. I can do it.

Note that in order to achieve single crystallization in the (100) plane, the semiconductor layer may be formed so as to span both the superconductor and the insulating film.

[Embodiments of the invention]

Embodiments of the present invention will be described in detail below with reference to the drawings.

FIG. 1 is a sectional view showing a part of a superconducting element according to an embodiment of the present invention. An insulating film 2 made of SiO with a thickness of approximately 700 nm is formed by thermally oxidizing a (100) oriented Si substrate 1.
form. Next, a NbN thin film with a thickness of about 20 nm was formed by reactive sputtering using a mixed gas of Ar and N2, and a CF film was formed using the photoresist pattern as a mask.
An electrode 3 made of a superconductor was formed by processing using a reactive ion etching method using four gases. The distance between opposing electrodes is preferably selected to be 0.5 to 0.1 μm. Next, polycrystalline or amorphous S is grown by vapor phase growth.
I is deposited to a thickness of about 20 nm and etched using CF and gas using the photoresist pattern as a mask. Subsequently, using a sputtering method, Sin, which is not shown in the figure, is
After the film was deposited to a thickness of about 30 nm, it was heated to 500° C. to 1500° C. using a laser beam or a heater to increase the crystal grain size of the semiconductor or to form a single crystal, thereby forming the semiconductor layer 4. After this heat treatment, the 5in2 film is removed by etching. The shape of the semiconductor layer 4 is the second
As shown in the figure, the electrode @S is determined so as to extend over both the insulating film 2 and the electrode 3, including the area other than the opposing area 5. By doing so, the crystal orientation of the semiconductor layer 4 after recrystallization can be set to the (100) plane. The fact that the crystal orientation can be aligned to the (100) plane means that
This is effective for reducing variations in device characteristics.

Next, an insulator layer 6 with a thickness of about 1100 nm is formed by depositing Sin on the surface of the semiconductor layer 4 or by self-oxidation of the semiconductor layer 4, and finally a control electrode made of an NbN thin film with a thickness of about 400 nm is formed. did. In addition to self-oxidation, this insulating layer 6 may be formed by depositing a low insulating material. Through the above steps, the superconducting element of the present invention could be realized.

In the above embodiments, NbN was used as the material for the electrode 3. FIG. 3 shows changes in superconducting transition temperature Tc, which is an important indicator of superconducting properties, between an NbN thin film and a conventional Nb thin film due to heat treatment. In contrast to the Nb thin film, where Tc decreases and the superconducting properties deteriorate, NbN#
Ill does not have this problem. Instead of NbN,
Nb,,Si.

N b s G e , M o N , V a S
A similar effect could be obtained when i was used.

In addition to Si, semiconductor materials include Ga As,
I n A s , I n P +InSb, Ga
It goes without saying that materials such as P, Ge, and CdS may also be used. Further, although a superconductor is used as the control electrode in the above embodiment, a normal conducting metal such as AQ or a semiconductor containing impurities may also be used. Further, although an insulating film is formed on the substrate, the insulating film can be omitted if the substrate material is quartz or Si with few impurities that does not show conductivity at extremely low temperatures. Although FIG. 1 shows a superconducting transistor in which two electrodes 3 face each other and has a control electrode, there is also a planar Josephson element with the electrodes 3 as they are but without a control electrode.

Alternatively, a super Schottky diode having only one electrode 3 may be formed and a circuit may be formed using this.

The superconducting element manufactured in this way was heated with liquid helium.
When operated with cooling, the circuit is electrically isolated from the element power (substrate force), so the substrate capacitance is small and switching is fast. Furthermore, since the crystallinity of the semiconductor layer can be improved and the crystal orientation can be aligned when it is made into a single crystal, variations in device characteristics can be reduced and highly integrated circuits can be manufactured at a high yield.

〔Effect of the invention〕

According to the present invention, since the semiconductor layer in contact with the superconductor is insulated from the substrate and has no substrate capacitance, the switching speed of the superconducting element can be increased.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view showing a part of a superconducting device according to an embodiment of the present invention, FIG. 2 is a top view showing a part of the manufacturing process of a superconducting device according to an embodiment of the present invention, and FIG. FIG. 3 is an explanatory diagram showing changes in characteristics of a superconducting electrode. 1... Substrate, 2... Insulating film, 3... Electrode, 4...
- Semiconductor layer, 6... Insulator film, 7... Control electrode.

Claims (1)

[Claims] 1. An electrode made of a superconductor provided on a substrate, a semiconductor layer formed on the electrode, an insulating layer formed on the semiconductor layer, and an insulating layer formed on the insulating layer. 1. A superconducting element comprising at least a control electrode made of metal or semiconductor. 2. A superconducting element according to claim 1, further comprising an insulating film between the substrate and the electrode made of a superconductor. 3. A superconducting element according to claim 1 or 2, wherein the superconductor forming the electrode is made of a material selected from NbN, Nb_3Si, Nb_3Ge, MoN, and V_3Si. 4. A superconducting element according to any one of claims 1 to 3, wherein the semiconductor layer is a heat-treated amorphous or polycrystalline semiconductor thin film. 5. A superconducting element according to any one of claims 1 to 4, wherein the semiconductor layer is formed to span both the electrode and the insulating film and cover the upper surface thereof. .