JPH04134885A - 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 gate electrode 4, which forms the extremely thin superconducting channel 10. However, its thickness is not sufficient for a source region and a drain region. To comply with this, ions are implanted with the electrode 4 as a mask formed on the superconducting channel, thereby forming an oxide superconductor layer, which is used as a superconducting source and a superconducting drain region.

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, 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 a low-power consumption, high-speed operation element that utilizes 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 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 has a superconducting source electrode 4 due to the superconducting proximity effect.
1 and the superconducting current flowing through the semiconductor layer 43 between the superconducting drain electrode 42 by controlling the superconducting current with a gate voltage;
It is a high-speed operating element.

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 superconducting proximity effect, the superconducting FET has a superconducting source electrode 41 and a superconducting drain electrode 42.
must be made 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 superconducting F using oxide superconductors
ET 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, a superconducting channel formed of an oxide superconducting thin film formed on a substrate, a superconducting source region and a superconducting drain region arranged on both sides of the superconducting channel, 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 gate electrode that is arranged on the superconducting channel via an insulating layer and controls the current flowing in the superconducting channel. There is provided a superconducting element comprising: the superconducting source region and the superconducting drain region being formed in the substrate.

In addition, in the present invention, as a method for producing the above superconducting element, a layer of a compound that becomes an oxide superconductor is formed on the surface of an insulating substrate by implanting oxygen ions, or a layer of a compound that becomes an oxide superconductor is formed by implanting oxygen ions. After forming a thin oxide superconducting thin film on a semiconductor substrate having a superconducting layer on the surface and an insulating film as an underlying layer, and forming a gate electrode on a portion of the oxide superconducting thin film that will become a superconducting channel, A method for manufacturing a superconducting element is provided, which includes a step of implanting ions using the gate electrode as a mask to form the superconducting source region and the superconducting drain region in the oxide layer.

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 a conventional superconducting FET uses 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 m conductor. 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.

The method of the invention uses a substrate whose surface is provided with a layer of a compound that becomes an oxide superconductor by implantation of oxygen ions. Then, an oxide superconducting thin film having a thickness of about 5 nm is first formed on the above substrate. To form such ultra-thin oxide superconducting thin films, it is common to strictly control the growth rate and film formation time of the thin film, and this method is preferable when using sputtering method etc. . However, since the oxide superconductor crystal has a crystal structure in which each constituent element is stacked in layers, it is also preferable to stack up an appropriate number of unit cells of the oxide superconductor using the MBE (molecular beam epitaxy) method.

Although the ultrathin oxide superconducting thin film described above has a preferred thickness for a superconducting channel, it is insufficiently thick for source and drain regions. Therefore, the superconducting layers in the source and drain regions must be made thicker. In order to thicken the superconducting layer in the source and drain regions while keeping the thickness of the superconducting channel portion as it is, the method of the present invention implants ions using the gate electrode formed on the superconducting channel as a mask. An oxide superconductor layer is formed in the substrate to serve as a superconducting source region and a superconducting drain region.

In the superconducting element of the present invention, an oxide single crystal substrate such as MgO1SrTIO3, which has a layer of a compound that becomes an oxide superconductor by implanting oxygen ions on its surface, can be used as the substrate. These substrates are preferable because it is possible to grow an oxide superconducting thin film made of highly oriented crystals. In addition, MgAl2O is added to the lower layer of the above compound.
It is also preferred to use a Si substrate with a layer of < and BaTiO3.

The superconducting element of the present invention includes a Y-Ba-Cu-0 based oxide superconductor, a Bi-5r-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.
It has an ultra-thin oxide superconducting thin film 1 of nm thickness.

Almost at the center of the oxide superconducting thin film 1 is a superconducting channel l.
A gate electrode 4 is formed on the superconducting channel 10 with an insulator 6 in between.

On both sides of the superconducting channel 10 in the substrate 5, a superconducting source region 12 and a superconducting drain region 13 having a thickness of about 200 nm are formed continuously from the oxide superconducting thin film 1. A source electrode 2 and a drain electrode 3 are provided on the superconducting source region 12 and the superconducting drain region 13, respectively.

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 a substrate 5 as shown in FIG. 2(a), which has a Y+Ba2Cu307-y layer 50 formed by sputtering or the like, an extremely thin Y+BaaCu30 layer 50 of about 5 nm is deposited on the surface of the substrate 5 as shown in FIG. 2(a).
The t~8 oxide superconducting thin film 1 is formed by a method such as an oxidative sputtering method, a reactive vapor deposition method, an MBE method, or a CVD method. YJa2Cu+07-Y is Y1Ba2Cu3
When compared with 0q-U oxide superconductor, it is an oxide that has the same constituent elements and exhibits insulating properties with a small number of oxygen in the crystal when y>x, and can be easily converted into YIBa by oxygen ion implantation.
2Cu+ Ch-x becomes an oxide superconductor. The substrate 5 is made of Mg0 (10
0) substrate, an insulating substrate such as a 5rTtC1+ (100) substrate, or a semiconductor substrate such as 31 having an insulating film under the oxide layer 50 on the surface is preferable. This 81 board is
It is preferable to have a layer of MgA120n formed by a CVD method and a BaTiO3 layer formed by a sputtering method as a layer below the oxide layer 50.

Examples of oxide superconductors include Y-Ba-Cu-○-based oxide superconductors, Bi-5r-Ca-Cu-0-based oxide superconductors, and TI-Ba-Ca-Cu-0-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), an insulating film 16 is laminated on the oxide superconducting thin film 1. The thickness of the insulating film 16 is set to 1Q nm or more. It is preferable to use an insulator such as MgO for the insulating film 16 that does not create a large level at the interface with the oxide superconducting thin film. A metal layer 14 for a gate electrode is laminated on the insulating film 16 as shown in FIG. For the metal layer 14, it is preferable to use a high melting point metal such as ^U, T1, or W, or a silicide thereof.

Unnecessary portions of this metal film 14 are removed by etching or the like and processed into a gate electrode 4 as shown in FIG. 2(e). Leaving the insulating film 16 as it is, oxygen ions are implanted using the gate electrode 4 formed as described above as a mask.
A part of the oxide layer 50 is made into a superconductor.

After performing the above ion implantation at an implantation energy of 150 keV or less, a heat treatment was performed in which the substrate 5 was heated to 450° C. and held at that temperature for 30 minutes. As a result of this heat treatment, a superconducting source region 12 and a superconducting drain region 1 that are continuous with the oxide superconducting thin film 1 are formed in the oxide layer 50 of the substrate 5 other than below the gate electrode 4, as shown in FIG. 2(f).
3 is formed. Further, a portion of the oxide superconducting thin film 1 below the gate electrode 4 becomes a superconducting channel 10.

Instead of the ion implantation-heat treatment process described above, it is also possible to form the superconducting source region 12 and the superconducting drain region 13 by performing focused ion beam irradiation. In this case, when irradiating with a focused ion beam, it is preferable to irradiate oxygen ions with an irradiation energy of 150 keV or less.

After the superconducting source region 12 and superconducting drain region 13 are formed, as shown in FIG. 2(g'), the insulating film 1 is
Unnecessary portions of 6 are removed to form an insulating layer 6.

At this time, side etching is promoted as necessary, and the insulating layer 6
shorten the length of Finally, similarly to the gate electrode 4, Au
Alternatively, using 7iSW and these silicides, the source electrode 2 and the drain electrode 3 are formed on the superconducting source region 12 and the superconducting drain region 13, respectively.

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 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 superconducting thin film, 2... Source electrode, 3... Drain electrode, 4... Gate electrode, 5... Substrate

Claims (2)

[Claims] (1) A superconducting channel formed of an oxide superconducting thin film formed on a substrate, a superconducting source region and a superconducting drain region arranged on both sides of the superconducting channel, and above the superconducting source region and the superconducting drain region. a source electrode and a drain electrode arranged in the superconducting channel to flow a current through the superconducting channel, and a gate electrode arranged on the superconducting channel via an insulating layer to control the current flowing in the superconducting channel, the superconducting source region and A superconducting element, characterized in that a superconducting drain region is formed in the substrate. (2) In the method for producing a superconducting element according to claim 1, a compound that becomes an oxide superconductor by implanting oxygen ions on an insulating substrate having a layer of a compound that becomes an oxide superconductor by implanting oxygen ions on its surface; After forming a thin oxide superconducting thin film on a semiconductor substrate having a layer of A method for manufacturing a superconducting element, comprising the steps of: implanting ions using the gate electrode as a mask to form the superconducting source region and the superconducting drain region in the oxide layer.