JPH04134887A - Superconducting device and manufacture thereof - 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 superconducting circuit with gate voltage. CONSTITUTION:A gate electrode 4 is installed to a superconducting device in order to control a superconducting channel 10 by an oxide superconductor, a source electrode 2 which passes electric current thereto, a drain electrode 3, and electric current flowing in the superconducting channel. The main current flows in the superconductor. The channel 10 is turned on and off with voltage applied to the electrode 4, which calls for a superconducting channel with an extremely thin thickness. The thickness is arranged to be sufficient for a superconducting source region and a superconducting drain region. The oxide thin film is heat-treated in an oxygen atmosphere so as to diffuse oxygen from the surface, thereby forming the channel 10. The oxide superconductor may lose its superconductivity due to the number of oxygen in the crystal. Therefore, oxygen ions are implanted into a part which forms a superconducting region or the conductor is heat-treated in the oxygen atmosphere so as to diffuse the oxygen, thereby producing the superconductor.

Description

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

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, as three-terminal elements using superconductivity, there are superconducting base transistors, superconducting FETs, etc. FIG. 3 shows a conceptual diagram of a superconducting paste transistor. The superconducting base transistor shown in FIG. 3 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. The collector 25 has a structure in which the collectors 25 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. 4 shows a conceptual diagram of a superconducting FET. In the superconducting FET of FIG. 4, a superconducting source electrode 41 and a superconducting drain electrode 42 made of a superconductor are connected to a semiconductor layer 43
are placed close to each other on top. The lower part of the semiconductor layer 43 between the superconducting source electrode 41 and the superconducting drain electrode 42 is largely shaved off and its thickness is reduced. Further, a gate insulating film 46 is formed on the lower surface of the semiconductor layer 43.
is formed, and a gate electrode 44 is provided and visible on the gate insulating film 46.

A superconducting FET is an element that operates at high speed with low power consumption and controls 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 of 1, 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 superconducting FETs using oxide superconductors
could not be produced 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 Accordingly, an object of the present invention is to provide a superconducting element having a novel configuration and a method for manufacturing the same, 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. In a superconducting element comprising a gate electrode that controls a flowing current, the superconducting channel has the same constituent elements as the oxide superconductor constituting the oxide superconducting thin film below the superconducting channel, and has a higher oxygen content than the oxide superconductor. SUMMARY OF THE INVENTION A superconducting device is provided that includes an insulating region with a reduced amount of oxide.

Further, in the present invention, as a method for producing the above-mentioned superconducting element, 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; After forming the gate electrode on the oxide thin film,
forming the superconducting source region and the superconducting drain region by implanting oxygen ions, ions, and heat-treating the oxide thin film in an oxygen atmosphere to diffuse oxygen and form a superconducting channel below the gate electrode; A method for manufacturing a superconducting element is provided, the method comprising the steps of:

Function The superconducting element of the present invention includes a superconducting channel made of an oxide superconductor, a source electrode and a drain electrode that allow current to flow through the superconducting channel, and a gate electrode that controls the current flowing through the superconducting channel. In the superconducting element of the present invention, each electrode does not necessarily have to be a superconducting electrode.

Further, while conventional superconducting FETs use the superconducting proximity effect to cause a superconducting current to flow through the semiconductor, in the superconducting element of the present invention, the main current flows through the superconductor. Therefore, restrictions on microfabrication techniques required when manufacturing conventional superconducting FETs are relaxed.

The superconducting channel must be approximately 5 nm thick 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 approximately 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 having a small number of oxygen in the crystal, in fact, an oxide having the same constituent elements as the oxide superconductor and a lower amount of oxygen than the oxide superconductor. A thin film is formed, and oxygen ions are implanted into a portion of the thin film that will become a superconducting region, or heat treatment is performed in an oxygen atmosphere to diffuse oxygen and form 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 superconducting device of the present invention, the thickness of the superconducting source region and the superconducting drain region should be about 200 nm, 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.

The superconducting element of the present invention is MgO1SrTi○3, [:dN
Preferably, it is manufactured on an oxide single crystal substrate such as dA104. These substrates are preferable because it is possible to grow the above-mentioned oxide thin film made of highly oriented crystals. In addition, MgA], 04, BaT on the surface
It is also preferable to use a Si substrate coated with iO3 or the like.

The superconducting element of the present invention includes a Y-Ba-Cu-0 based oxide superconductor, a Bi-3r-Ca-Cu-○ based oxide superconductor, and a TI-Ba-Ca-Cu-0 based oxide superconductor. Any oxide superconductor 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 FIG. 1 shows a cross-sectional view of the superconducting element of the present invention.

The superconducting element shown in FIG. 1 is formed in a thin film 11 of an insulating oxide that has the same constituent elements as the oxide superconductor deposited on the substrate 5 and has a lower oxygen content than the oxide superconductor. It has a superconducting channel 10, a superconducting source region 12, and a superconducting drain region 13. There is an insulating region 50 on the underside of the superconducting channel 10, and the thickness of the superconducting channel 10 is approximately 5 nm.

A gate electrode 4 is formed on the superconducting channel 10 via an insulating layer 6 such as SiN. Superconducting channel 10
A superconducting source region 12 and a superconducting drain region 13 having a thickness of about 200 nm are formed on both sides of the superconducting region. Superconducting source region 12 and superconducting drain region 13
A source electrode 2 and a drain electrode 3 are respectively provided on the top. The source electrode 2, the drain electrode 3, and the gate electrode 4 are all made of Au, a high melting point metal such as Ti, or W, or a silicide thereof.

Referring to FIG. 2, the procedure for manufacturing the superconducting element of the present invention using the method of the present invention will be described. First, about 200 nm was applied to the surface of the substrate 5 as shown in FIG. 2(a), as shown in FIG. 2(b).
A Y, Ba2Cu307-, oxide thin film 11 having a thickness of about m is formed by an oxidation sputtering method.

Y 1 B a 2 CL120? -Y oxide is
Compared to Y1Ba2Cu30i-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% O2: 1
0% Pressure 10 Pa Substrate temperature 700°C As the substrate 5, Mg0 (100) substrate, 5rTt03
(100) Substrate, CdNdA10. An insulating substrate such as (001) or a semiconductor substrate such as 81 having an insulating film on the surface is preferable. The surface of the second 81 substrate is MgAl2O4.
, BaTiO3, etc. are preferably laminated by a sputtering method.

Examples of oxide superconductors include Y-Ba-Cu-0-based oxide superconductors, Bi-3r-Ca-Cu-0-based oxide superconductors, and Tl-Ba-Roa=cu-0-based oxide superconductors. A thin film with C-axis orientation is preferred.

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. 2(C), Si is placed on the oxide thin film 11.
An insulating film 16 made of N or the like is formed. The thickness of the insulating film 16 is approximately 1
The thickness should be such that tunnel current of 0 nm or more can be ignored.

In addition, it is preferable to use an insulator that does not create a large level at the interface with the oxide superconducting thin film for the insulating film 16, and from the viewpoint of reducing mechanical stress, an insulating film having a composition similar to that of the oxide superconductor is used continuously. It is also preferable to form.

A metal film 17 for a gate electrode is laminated on the insulating film 16 as shown in FIG. 2(d). As described above, this metal film 17 is formed of Au, a high melting point metal such as T1, W, etc., or a silicide thereof. A gate electrode pattern is formed on the metal film 17 using photoresist films 91, 92, and 93 as shown in FIG. 2(e). Metal film 17 and insulating film 16
The gate electrode 4 is etched as shown in FIG. 2(f).
and an insulating layer 6 is formed. When etching the insulating film 16, side etching is promoted as necessary to reduce the length of the insulating layer 6.

After forming the gate electrode 4 and the insulating layer 6, anisotropic etching is performed using Ar ion milling or the like as shown in FIG.
Grooves 14 and 15 of Qnm are formed. The metal films and insulating films other than the gate electrode 4 and the insulating layer 6 are removed, and the structure shown in FIG.
Oxygen ions are implanted into the oxide thin film 11 as shown in
A superconducting source region 12 and a superconducting drain region 13 are formed. The oxygen ion implantation conditions are shown below.

Acceleration voltage 40kV Injection amount (dose) 1 x 10'5 ~ 1 x 1016 pieces/
After forming the CRL superconducting source region 12 and the superconducting drain region 13, as shown in FIG. and a drain electrode 3 is formed. Photoresist film 92
A film 1 made of the same material as the source electrode 2 and drain electrode 3 is also formed on the top.
7 is formed, but it is removed at the same time as the photoresist film 92.

Finally, heat treatment is performed to diffuse oxygen into the oxide thin film through the gaps between the source electrode 2, drain electrode 3, and insulating film 6, thereby forming the superconducting channel 1 as shown in FIG. 2(j).
form 0. The heat treatment conditions are shown below.

Substrate temperature 350℃ Oxygen partial pressure lX10’Pa Holding time 1 hour The underside of the superconducting channel 10 becomes an insulating region 50.

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.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram of the superconducting device of the present invention, FIG. 2 is a schematic diagram showing the steps for producing the superconducting device of the present invention by the method of the present invention, and FIG. 3 is a schematic diagram of the superconducting device of the present invention. FIG. 4 is a schematic diagram of a base transistor; FIG. 4 is a schematic diagram of a superconducting FET. Main reference numbers: 2...source electrode, 3...drain electrode, 4...gate electrode, 5...substrate

Claims (2)

[Claims] (1) A superconducting channel formed of an oxide superconductor,
A superconducting source region and a superconducting drain region, which are arranged on both sides of the superconducting channel and are made of an oxide superconductor constituting the superconducting channel, and which are arranged on the superconducting source region and the superconducting drain region, and which supply current to the superconducting channel. A superconducting element comprising a source electrode and a drain electrode through which current flows, and a gate electrode disposed over the superconducting channel via an insulating layer to control the current flowing through the superconducting channel, wherein the oxide superconducting 1. A superconducting element comprising an insulating region made of an oxide that has the same constituent elements as an oxide superconductor constituting a thin film and has a lower oxygen content than the oxide superconductor. (2) In the method for producing a superconducting element according to claim 1, 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, After forming the gate electrode on the oxide thin film,
a step of implanting oxygen ions to form the superconducting source region and the superconducting drain region; and a step of heat-treating the oxide thin film in an oxygen atmosphere to diffuse oxygen to form a superconducting channel below the gate electrode. A method for producing a superconducting element, comprising: