JPH04134888A - Manufacture of superconducting device - Google Patents

Abstract

PURPOSE:To make it possible to eliminate the need for a fine processing technology and prepare a high performance device which uses an oxide superconductor by controlling a superconducting current flowing in a superconduction circuit with gate voltage. CONSTITUTION:At first, when compared with an oxide insulator, a thin film of an insulator with a smaller amount of oxygen is formed. Then, oxygen ions are implanted in this thin film so as to form a superconducting source and a superconducting drain region. Furthermore, they are heat-treated in the oxygen atmosphere and oxygen is diffused so that a conduction channel 10 may be formed. Then, a source electrode 2, a drain electrode 3, and a gate electrode 4 are formed thereon. The current which flows in the superconducting channel 10 between the electrodes 2 and 3 is controlled with voltage applied to the electrode 4. The channel 10 is turned on and off with the voltage applied to the electrode 4, which calls for the superconducting channel 10 with an extremely thin film. Oxygen ions are implanted into a part which becomes a superconducting region where a thin film has been formed.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a method for producing a superconducting element. More specifically, the present invention relates to a novel method for manufacturing superconducting elements.

A Josephson device is a typical device using conventional technology superconductivity. A Josephson device has a configuration in which a pair of superconductors are coupled via a tunnel barrier, and is capable of high-speed switching operation. However, the Josephson element is 2
It is a terminal element and requires a complicated circuit configuration to realize a logic circuit.

On the other hand, three-terminal elements using superconductivity include superconducting base transistors, superconducting FETs, and the like. In Figure 2,
A conceptual diagram of a superconducting base transistor is shown. The superconducting base transistor shown in FIG. 2 is composed of an emitter 21 made of a superconductor or a normal conductor, a tunnel barrier 22 made of an insulator, a base 23 made of a superconductor, a semiconductor isolator 24, and a normal conductor. collector 2
It has a structure in which 5 layers are stacked. This superconducting base transistor is an element that operates at high speed with low power consumption using high speed electrons that have passed through the tunnel barrier 22.

FIG. 3 shows a conceptual diagram of a superconducting FET. In the superconducting FET shown in FIG. 3, a superconducting source electrode 41 and a superconducting drain electrode 42 made of a superconductor are connected to a semiconductor layer
are placed close to each other on top. The semiconductor layer 43 in the portion between the superconducting source electrode 41 and the superconducting drain electrode 42 has its lower side largely shaved and has a reduced thickness.

Further, a gate insulating film 46 is formed on the lower surface of the semiconductor layer 43, and a gate electrode 44 is provided on the gate insulating film 46.

A superconducting FET is an element that operates at high speed with low power consumption and controls a superconducting current flowing through a semiconductor layer 43 between a superconducting source electrode 41 and a superconducting drain electrode 42 by a gate voltage due to the proximity effect.

Furthermore, a three-terminal superconducting element has been announced in which a channel is formed between a source electrode and a drain electrode using a superconductor, and the current flowing through this superconducting channel is controlled by a voltage applied to a gate electrode.

Problems to be Solved by the Invention The above-described superconducting base transistor and superconducting FET both have a portion in which a semiconductor layer and a superconductor layer are laminated. However, it is difficult to fabricate a stacked structure of a semiconductor layer and a superconductor layer using oxide superconductors, which have been studied in recent years. Moreover, even if this structure could be fabricated, it was difficult to control the interface between the semiconductor layer and the superconductor layer, and the device did not operate satisfactorily.

Furthermore, in order to utilize the proximity effect, the superconducting FET must be manufactured so that the superconducting source electrode 41 and the superconducting drain electrode 42 are located close to each other within several times the coherence length of the superconductor that constitutes each. In particular, an oxide superconductor has a short coherence length, so when an oxide superconductor is used, the distance between the superconducting source electrode 41 and the superconducting drain electrode 42 must be several lQnm or less. Such microfabrication is extremely difficult, and conventionally it has not been possible to fabricate superconducting FETs using oxide superconductors with good reproducibility.

Furthermore, superconducting devices with conventional superconducting channels are
Although modulation operation was confirmed, complete on/off operation was not possible due to the high carrier density. Since oxide superconductors have a low carrier density, it is expected that by using them for superconducting channels, it will be possible to realize the above-mentioned devices that perform perfect on/off operation. However, the thickness of the superconducting channel must be approximately 5 nm, making it difficult to realize such a configuration.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a novel method for manufacturing a superconducting element in which the superconducting current flowing in a superconducting channel is controlled by a gate electrode, which solves the problems of the prior art described above.

Means for Solving the Problems According to the present invention, there is provided a superconducting channel formed of an oxide superconductor, and a superconducting source region disposed on both sides of the superconducting channel and composed of the oxide superconductor constituting the superconducting channel. and a superconducting drain region, a source electrode and a drain electrode that are arranged on the superconducting source region and the superconducting drain region and allow current to flow through the superconducting channel, and a source electrode and a drain electrode that are arranged on the superconducting channel with an insulating layer interposed therebetween and that flow into the superconducting channel. an oxide having the same constituent elements as the oxide superconductor constituting the oxide superconductor thin film and having a lower amount of oxygen than the oxide superconductor below the superconducting channel; In a method for producing a superconducting element having an insulating region according to
forming a thin oxide film having a lower oxygen content than the oxide superconductor, and implanting oxygen ions into the oxide thin film to form the superconducting source region and the superconducting drain region; A method for manufacturing a superconducting element is provided, which includes the step of forming a superconducting channel by performing heat treatment in an oxygen atmosphere to diffuse oxygen, and then manufacturing the source electrode, drain electrode, and gate electrode.

Operation In the method of the present invention, first a thin film of an oxide of an insulator having the same constituent elements as the oxide superconductor and a lower amount of oxygen than the oxide superconductor is formed. Next, oxygen ions are implanted into this thin film to form a superconducting source region and a superconducting drain region. After further heat treatment in an oxygen atmosphere to diffuse oxygen and form a superconducting channel, a source electrode, a drain electrode, and a gate electrode are produced.

A superconducting element targeted by the method of the present invention has a configuration in which a superconducting current flowing through a superconducting channel between a source electrode and a drain electrode is controlled by a voltage applied to a gate electrode.

The superconducting channel must have a thickness of about 5 nm in the direction of the electric field generated by the gate electrode in order to be opened and closed by the voltage applied to the gate electrode. The main focus of the present invention is to realize such an ultra-thin superconducting channel.

In the method of the present invention, first, a thin film of an oxide having a thickness of about 200 to 300 nm and having the same constituent elements as the oxide superconductor and a lower amount of oxygen than the oxide superconductor is formed.

This thin oxide film is preferably formed on the substrate and has a thickness sufficient to cover the superconducting source and drain regions.

Oxygen ions are implanted into this oxide thin film to form a superconducting source region and a superconducting drain region. Further, this oxide thin film is heat-treated in an oxygen atmosphere to diffuse oxygen from the surface and form a superconducting channel. The number of oxygen atoms in the crystal of an oxide superconductor is unstable and can be changed by heat treatment or the like. In addition, the properties of oxide superconductors tend to change depending on the number of oxygen in the crystal.
In particular, if the number of oxygen is lower than the appropriate value, the critical temperature will drop significantly or the superconductivity will be lost.

Therefore, in the method of the present invention, an oxide superconductor with a small amount of oxygen in the crystal, in fact, an oxide that has a solid constituent element with the oxide superconductor and has a smaller amount of oxygen than the oxide superconductor. A thin film is formed, and oxygen ions are implanted into the part of this thin film that will become the superconducting region, or heat treatment is performed in an oxygen atmosphere to diffuse oxygen and make it a superconductor. By adjusting the oxygen ion acceleration voltage, oxygen partial pressure, treatment temperature, treatment time, etc., it is possible to form an oxide superconductor to have an arbitrary thickness. Further, since oxygen tends to move in the direction perpendicular to the C-axis of the crystal in an oxide superconductor, it is also preferable to form grooves parallel to the C-axis of the crystal in the portion of the oxide thin film where oxygen is diffused, and then heat-treat the groove.

In the above superconducting device, the thickness of the superconducting source region and the superconducting drain region should be about 2001 m, and the thickness of the superconducting channel should be about 5 nm.

Therefore, in the method of the present invention, the above oxide thin film is
It is formed to a thickness of 0 nm, and oxygen is implanted into the portions that will become the superconducting source region and the superconducting drain region. Also,
Since the superconducting channel portion is extremely thin at 5 nm, oxygen is diffused through heat treatment to make it a superconductor.

In the method of the present invention, the above oxide thin film is MgO1SrT
It is preferable to fabricate on an oxide single crystal substrate such as i03 or CdNdAlO4. These substrates are preferable because it is possible to grow an oxide thin film made of highly oriented crystals. In addition, MgA1201 on the surface
It is also preferable to use a Si substrate coated with , BaTiO3 or the like.

In the present invention, any oxidized Physical superconductors can be used.

EXAMPLES Hereinafter, the present invention will be explained in more detail with reference to Examples, but the following disclosure is merely an example of the present invention and does not limit the technical scope of the present invention in any way.

EXAMPLE Referring to FIG. 1, the procedure for manufacturing the superconducting element of the present invention by the method of the present invention will be explained. First, on the surface of the substrate 5 as shown in FIG. 1(a), about 20
A Y1Ba2[u307-7 oxide thin film 11 with a thickness of approximately nm is formed by an offset sputtering method.

YIBa2Cu30i-y oxide is Y, Ba2CU3
Compared to 07-X oxide superconductor, it exhibits insulating properties at low temperatures when y>x. The film-forming conditions for forming the oxide thin film 11 by the off-axis sputtering method are shown below.

Sputtering gas Ar:90%02:1
0% Pressure 10 Pa Substrate temperature 700°C As the substrate 5, Mg0 (100) substrate, 5rTiO3
A (100) substrate, an insulating substrate such as CdNdAlO4 (001), or a semiconductor substrate such as 81 having an insulating film on the surface is preferable. MgA on the surface of this 81 substrate! , ○.

And BaT+03 is preferably laminated by sputtering method.

Examples of oxide superconductors include Y-Ba-Cu-0-based oxide superconductors, B+ -3r -Ca-Cu-〇-based oxide superconductors, and TI-Ba-Ca-Nime-○-based oxide superconductors. is preferable, and a thin film with C-axis orientation is preferable.

This is because the C-axis oriented oxide superconducting thin film has a large critical current density in the direction parallel to the substrate.

Next, as shown in FIG. 1C, a gate electrode pattern is formed on the oxide thin film 11 using a photoresist film 91.

From above this pattern, the exposed portion of the oxide thin film 11 is etched with 5 to 1Q nm of Ar ion etching, as shown in FIG. 2(d). The etching conditions are a substrate temperature of 100℃ and an acceleration voltage of 3.
kV.

Oxygen ions are implanted into the oxide thin film 11 to form the oxide thin film 1.
As shown in FIG. 1(e), a superconducting source region 12 and a superconducting drain region 13 are formed in 1. As shown in FIG. The oxygen ion implantation conditions are shown below.

Acceleration voltage 40kV Injection amount (dose amount) 1 x 1015 to 1 x 1016 pieces/
The CNF photoresist film 91 is removed and heat treated in an oxygen atmosphere to diffuse oxygen into the surface of the oxide thin film and the grooves 14 and 15, thereby forming a superconducting chimanel 10 as shown in Fig. 1). The heat treatment conditions are shown below.

Substrate temperature 350℃ Oxygen partial pressure I XIO' Pa Holding time 1 hour The underside of the superconducting channel 10 becomes an insulating region 50.

In this way, the superconducting channel 10, the superconducting source region 12
and oxide thin film 1 forming superconducting drain region 13
As shown in FIG. 1(g), an insulating film 16 made of SiN or the like is laminated on top of the insulating film 16. The thickness of the insulating film 16 is set to be about 10 nm or more so that tunnel current can be ignored. Further, the insulating film 16 is
It is preferable to use an insulator that does not create a large level at the interface with the oxide superconducting thin film, and from the viewpoint of reducing mechanical stress, it is also preferable to continuously form an insulating film having a composition similar to that of the oxide superconductor.

A metal film 17 is formed on the insulating film 16 as shown in the circle of FIG. For the metal film 17, it is preferable to use a high melting point metal such as Au, Ti, or W, or a silicide thereof. The metal film 17 and the insulating film 16 are etched using reactive ion etching or the like to form the gate electrode 4 and the insulating layer 6 as shown in FIG. 1(1).

When etching the insulating film 16, side etching is promoted as necessary to reduce the length of the insulating layer 6.

Finally, as shown in FIG. 1(J), source electrode 2 and drain electrode 3 are formed on superconducting source region 12 and superconducting drain region 13, respectively, using the same material as gate electrode 4.

When the superconducting element of the present invention is manufactured by the method of the present invention, restrictions on microfabrication techniques required when manufacturing a superconducting FET are relaxed. Furthermore, since the surface can be made flat, it becomes easier to form wiring later as required. Therefore,
It is easy to manufacture, has stable device performance, and has good reproducibility.

As described in detail, the superconducting element of the present invention has a configuration in which the superconducting current flowing in the superconducting channel is controlled by the gate voltage. Therefore, like the conventional superconducting FET,
Since it does not utilize the superconducting proximity effect, microfabrication technology is not required. Furthermore, since there is no need to stack a superconductor and a semiconductor, high-performance devices can be manufactured using oxide superconductors.

The present invention further promotes the application of superconducting technology to electronic devices.

2 Main reference numbers:.

2...source electrode, 3...Drain electrode, 4...gate electrode, 5... Board

Claims (1)

[Claims] a superconducting channel formed of an oxide superconductor; a superconducting source region and a superconducting drain region disposed on both sides of the superconducting channel and composed of the oxide superconductor constituting the superconducting channel; a source electrode and a drain electrode disposed on the superconducting drain region to allow current to flow through the superconducting channel; and a gate electrode disposed on the superconducting channel via an insulating layer to control the current flowing in the superconducting channel; A method for producing a superconducting element comprising an insulating region made of an oxide having the same constituent elements as the oxide superconductor constituting the oxide superconducting thin film and having a lower oxygen content than the oxide superconductor below a superconducting channel. In this step, a thin film of an oxide having the same constituent elements as the oxide superconductor and a lower amount of oxygen than the oxide superconductor is formed, and oxygen ions are implanted into the oxide thin film to form the superconducting source region. and forming the superconducting drain region, and forming the source electrode, drain electrode, and gate electrode after heat-treating the oxide thin film in an oxygen atmosphere to diffuse oxygen and forming a superconducting channel. A method for producing a superconducting element characterized by: