JPH04165682A - Superconducting element and manufacture thereof - Google Patents

Abstract

PURPOSE:To dispense with a fine processing and to obtain a high-performance element manufactured using an oxide superconductor film by a method wherein a superconducting channel has a constituent element identical with that of the oxide superconductor film arranged under the lower part of the channel and is defined by an oxide insulating region having the amount of oxygen less than that of the oxide superconductor film. CONSTITUTION:An element has a superconducting channel 10, which has a constituent element identical with that of an oxide superconductor film formed on a substrate 5 and is formed in a non-conductive oxide thin film 1 having the amount of oxygen less than that of the oxide superconductor film and showing an insulation property at a low temperature, and superconducting source and drain regions 12 and 13. There is an insulating region 50 on the lower side of the channel 10 and a gate electrode 4 is formed on the channel 10 via a gate insulating layer 6 consisting of MgO, SiN or the like. The regions 12 and 13 are formed in the parts on both sides of the channel 10. Thereby, as a superconducting proximity effect is not utilized, a fine processing technique is unnecessary and the high-performance element can be manufactured using the oxide superconductor film.

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
Since it is a terminal element, it 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 3,
A conceptual diagram of a superconducting base transistor is shown. 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. 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. 4 shows a conceptual diagram of a superconducting FET. Superconducting FE in Figure 4? A superconducting source electrode 41 and a superconducting drain electrode 42 made of a superconductor are arranged close to each other on a semiconductor layer 43. 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 4 is formed on the gate insulating film 46.
4 is provided.

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 IQ nm 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 superconducting channel had to be approximately 5 nm thick, and it was 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 superconducting channel that is arranged on the superconducting channel with a gate insulating layer interposed therebetween. In a superconducting element comprising a gate electrode that controls a current flowing in the superconducting channel, the superconducting channel has the same constituent elements as the oxide superconductor constituting the superconducting channel disposed below, and has a higher content than the oxide superconductor. A superconducting element is provided that is defined by an insulating region made of an oxide with a low oxygen content.

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,
A step of implanting oxygen ions to form the superconducting source region and the superconducting drain region, and supplying electricity to the first electrode in an oxygen atmosphere to generate heat to diffuse oxygen into the oxide thin film to form the gate electrode. A method for manufacturing a superconducting element is provided, the method comprising the step of forming a superconducting channel under a superconducting channel.

Function The superconducting element of the present invention includes a superconducting channel made of an oxide superconductor, a superconducting source region and a superconducting drain region made of the oxide superconductor arranged at both ends of the superconducting channel, and a source electrode and a drain electrode that allow current to flow through the superconducting channel. , and a gate electrode for controlling the current flowing through the superconducting channel. In the superconducting element of the present invention, the superconducting channel is arranged below and has the same constituent elements as the oxide superconductor constituting the superconducting channel, and is formed by an insulating region made of an oxide having a lower amount of oxygen than the oxide superconductor. It is defined.

In order for the superconducting channel to be opened and closed by the voltage applied to the gate electrode, the grass must be approximately 5 nm thick in the direction of the electric field generated by the gate electrode.

In order to form the ultra-thin superconducting channel mentioned above, a thin film of oxide that has the same constituent elements as the oxide superconductor and a lower amount of oxygen than the oxide superconductor is deposited, and the thin film is placed in an oxygen atmosphere. There is a method of heat-treating and diffusing oxygen from the surface to transform the portion of this thin oxide film near the surface into a superconductor. 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, and especially when the number of oxygen is smaller than an appropriate value, the critical temperature decreases significantly or the superconductivity is lost.

In the above method, an oxide superconductor with a small number of oxygen in the crystal, which actually has the same constituent elements as the oxide superconductor,
A thin film of an oxide containing less oxygen than the oxide superconductor is formed, and heat treated in an oxygen atmosphere to diffuse oxygen to form a superconductor. Additionally, oxygen ions are implanted to convert deeper parts into superconductors. In this case, by adjusting the oxygen partial pressure, treatment temperature, treatment time, oxygen ion acceleration voltage, etc., it is possible to form the oxide superconductor to have an arbitrary thickness.

In the method of the present invention, the method is further improved, and the heating during the above heat treatment is performed by generating heat in the gate electrode. That is, a gate insulating layer and a gate electrode are formed at appropriate positions on the oxide thin film, and the gate electrode is energized to generate heat, thereby locally heating the portion of the oxide thin film directly below the gate electrode. . According to the method of the present invention, only the portion of the oxide thin film immediately below the gate electrode is locally heated, and oxygen is diffused only into that portion, thereby forming an oxide superconductor. Therefore, the position of the superconducting channel is automatically determined directly below the gate electrode.

In the method of the present invention, first, a thin film of an oxide having a thickness of about 200 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. After forming the superconducting source region and superconducting drain region, the above heat treatment is performed to form a superconducting channel. In addition, in oxide superconductors, the diffusion coefficient of oxygen in the direction perpendicular to the C-axis of the crystal is large, and oxygen moves easily in that direction. It is also preferable to process and heat treat.

The superconducting element of the present invention is a N1g○(100) substrate, SrT
iO2 (100) substrate, CdNdA10. (OO1)
It is preferable to fabricate on an oxide single crystal substrate such as a substrate. These substrates are preferable because it is possible to grow the above-mentioned oxide thin film made of highly oriented crystals. Also, on the surface λIgAlso< and BaT
It is also preferred to use a Si substrate coated with iO3.

The superconducting element of the present invention includes a Y-Ba, -Cu-0 based oxide superconductor, a T3]-3r-Ca-CU-0 based oxide superconductor, and a T1-Ba-Ca-Cu-○ based oxide superconductor. Any oxide superconductor can be used, such as a superconductor.

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 a non-superconducting oxide that has the same constituent elements as the oxide superconductor deposited on the substrate 5 and exhibits insulating properties at low temperatures with less oxygen content than the oxide superconductor. A superconducting channel 10, a superconducting source region 12 and a superconducting drain region 13 are formed in a thin film 1 of the present invention. There is an insulating region 50 on the underside of the superconducting channel 10, and the superconducting channel 10cD has a fineness of about 5 nm.

A gate electrode 4 is formed on the superconducting channel 10 via a gate insulating layer 6 made of MgO1SiN or the like. On both sides of the superconducting channel 10, a superconducting source region 12 and a superconducting drain region 13 with a thickness of about 200 nm are formed. A source electrode 2 and a drain electrode 3 are provided on the superconducting source region 12 and the superconducting drain region 13, respectively. The source electrode 2, drain electrode 3, and gate electrode 4 are all made of high melting point metals such as 8U, T1, W, or these metals.
It is formed by Iid.

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, on the surface of the substrate 5 as shown in FIG. 2(a), about 20
A Y, Ba2(:u+07-Y) oxide thin film 1 of approximately nm thickness is formed by an oxidation sputtering method.

¥1. Ba2CTo0,1 oxide is Y, Ba, 2C
Compared to the u+ Ch-x oxide superconductor, it exhibits insulating properties when y>x and has the same crystal structure. The film-forming conditions for forming the oxide thin film 1 by the off-axis sputtering method are shown below.

Sputtering gas Ar:90%02:10
% Pressure 10 Pa Substrate temperature 700°C As the substrate 5, Mg0 (100) substrate, 5rTi03
(100) substrate, CdNdAl0. An insulating substrate such as (001) or a semiconductor substrate such as Si having an insulating film on the surface is preferable. The surface of this 81 substrate was coated with &1gA1□0. A film is formed on which BaT i
Preferably, the O3 film is laminated by sputtering.

Examples of oxide superconductors include Y-Ba-Cu-0-based oxide superconductors, Bi-3r-Ca-Cu-0-based oxide superconductors, and TI-Ba-Ca-Cu-〇-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. 2(C), MgO
An insulating film 16 of 3iN or the like is formed. The thickness of the insulating film 16 is set so that a tunnel current of about IQ 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 14 for a gate electrode is laminated on the insulating film 16 as shown in FIG. 2(d). As described above, this metal film 14 is formed of Au, a high melting point metal such as T1, W, etc., or a silicide thereof. The metal film 14 and the insulating film 16 are etched by reactive ion etching, Ar ion milling, etc. to form the gate electrode 4 and the insulating layer 6 as shown in FIG. 2(e). 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, as shown in FIG.
), oxygen ions are implanted into the oxide thin film 1 to form a superconducting source region 12 and a superconducting drain region 13. The oxygen ion implantation conditions are shown below.

Accelerating voltage: 40 kV Dose: 1 x 10'5 to 1 x 10'6/crl After forming the superconducting source region 12 and superconducting drain region 13, anisotropic etching is performed using Ar ion milling, etc., as shown in Fig. 2(g). Then, the superconducting source region 12 and superconducting drain region 13 of the oxide superconductor are etched to expose the side surface of the portion 11 of the oxide thin film 1 below the gate insulating layer 6. Next, in an oxygen atmosphere, electricity is applied to the gate electrode 4 to generate heat, and oxygen is diffused into the portion 11 of the oxide thin film 1 below the gate insulating layer 6, thereby forming a superconducting channel 10 as shown in FIG. Form. In this case, the entire oxide thin film 1 is also heated if necessary. The heat treatment conditions are shown below.

Heating temperature: 350°C Oxygen partial pressure: 1×10'Pa Holding time: 1 hour Finally, as shown in FIG. After forming the electrode 2 and the drain electrode 3, the superconducting element of the present invention is completed.

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. Moreover, it is therefore easy to manufacture, the performance of the device is stable, and the reproducibility is good.

As described in detail, the superconducting element r of the present invention has a structure in which the superconducting current flowing in the superconducting channel is controlled by the gate voltage. Therefore, unlike conventional superconducting FETs, since the superconducting proximity effect is not utilized, microfabrication technology is not required. In other words, the superconducting element of the present invention does not require microfabrication technology to fabricate a pair of superconductor electrodes placed close to each other at a distance where the superconducting proximity effect occurs (several IQ nm or less in the case of oxide superconductors). . Furthermore, there is no need for the step of arranging an extremely thin tunnel barrier layer between the superconductor layers, which is necessary when manufacturing a Josephson device. Furthermore, since there is no need to laminate a superconductor and a semiconductor, high-performance devices can be manufactured using oxide superconductors.

The processing that requires the most precision in the superconducting element of the present invention is as follows:
Regarding the preparation and arrangement of the superconducting channel and gate insulating layer,
According to the method of the present invention, the self-line effect in which the gate insulating layer and the superconducting channel are automatically placed under the gate electrode can be utilized, so no microfabrication is required. Further, since the gate insulating layer is formed by removing oxygen by oxygen diffusion, it can be manufactured with good controllability.

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

[Brief explanation of the drawing]

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] 1... Oxide thin film, 2... Source electrode, 3... Drain electrode, 4... Gate electrode, 5... Substrate patent applicant,
Sumitomo Electric Industries, Ltd.

Claims (1)

[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 above the superconducting channel via a gate insulating layer to control the current flowing through the superconducting channel, wherein the superconducting channel is disposed below. A superconducting element defined by an insulating region made of an oxide having the same constituent elements as the oxide superconductor constituting the superconducting channel and having 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 applying electricity to the gate electrode in an oxygen atmosphere to generate heat to remove the oxidation 1. A method for manufacturing a superconducting device, comprising the step of diffusing oxygen into a thin film to form a superconducting channel below the gate electrode.