JPH04145672A - Superconductive element and method of producing the same - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

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 structure in which a pair of superconductors are coupled through 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 superconducting channel must have a thickness of 5 nm or less, 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 are provided a superconducting channel formed in an oxide superconducting thin film formed on a substrate, and source electrodes disposed near both ends of the superconducting channel to flow current through the superconducting channel. and a superconducting element comprising a drain electrode and a gate electrode disposed on the superconducting channel to control a current flowing through the superconducting channel, wherein the substrate has a protrusion, and the oxide superconducting thin film has a C-axis orientation. The oxide superconducting thin film is made of an oxide superconductor crystal, and a portion above the protrusion is made thin, the thin portion of the oxide superconducting thin film is the superconducting channel, and the source electrode and the drain electrode are oriented along the a-axis. Provided is a superconducting element comprising an oxide superconductor crystal of the present invention.

Further, in the present invention, as a method for manufacturing the above-mentioned superconducting element, on an insulating substrate on which a protrusion is formed or on a semiconductor substrate on which a protrusion is formed and has an insulating film on the surface,
forming a C-axis oriented oxide superconducting thin film with a thickness of 5 nm or less on the protrusion, etching portions of the C-axis oriented oxide superconducting thin film on both sides of the protrusion by 1Q nm or more;
A method for manufacturing a superconducting element is provided, which includes the step of forming a C-axis oriented oxide thin film on the etched portion.

Function The superconducting element of the present invention has a superconducting channel made of a C-axis oriented oxide superconducting thin film, a superconducting source electrode and a superconducting drain electrode made of C-axis oriented oxide superconducting thin films disposed on both sides of the superconducting channel, and a superconducting channel. and a gate electrode that controls the flowing current.

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 superconductor. Therefore, restrictions on microfabrication techniques required when manufacturing conventional superconducting FETs are relaxed.

The superconducting channel must have a thickness of 5 nm or less 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. In the superconducting element of the present invention, a portion of a C-axis oriented oxide superconducting thin film formed on a substrate provided with a protrusion, which is thinned by the protrusion of the substrate, serves as a superconducting channel.

If an oxide superconducting thin film is simply grown on a substrate with protrusions, a thin film of the same thickness will be formed on the protrusions, so the method of the present invention flattens the thin film surface after forming the thin film. , the portion of the thin film above the substrate protrusion is thinned;

Oxide superconductors generally have different superconducting properties depending on the crystal direction, and the critical current density is particularly large in the direction perpendicular to the C axis of the crystal. As a result, with conventional source and drain electrode structures, it is difficult to uniformly flow current through the ultrathin superconducting channel. In the superconducting device of the present invention, the superconducting source electrode and the superconducting drain electrode use a C-axis oriented oxide superconducting thin film, so the main current flows in a direction perpendicular to the substrate, and the superconducting channel is made of a C-axis oriented oxide superconducting thin film. Since a superconducting thin film is used, the flow is parallel to the substrate. That is,
In the superconducting element of the present invention, each of the superconducting source electrode, the superconducting drain electrode, and the superconducting channel is configured such that a main current flows in a direction where the critical current density of the oxide superconductor is high.

In the method of the present invention, the substrate temperature is set at about 700° C. to deposit the oxide superconducting thin film with the C-axis orientation of the superconducting channel. Further, the C-axis oriented oxide superconducting thin films of the source electrode and the drain electrode are formed at a substrate temperature of approximately 650° C. or lower during film formation. In either case, a sputtering method, an MBE (molecular beam epitaxy) method, a vacuum evaporation method, or the like can be used as a film forming method.

In the superconducting element of the present invention, the insulator substrate includes MgO
An oxide single crystal substrate such as 1SrTi03 can be used. These substrates are preferable because it is possible to grow an oxide superconducting thin film made of highly oriented oxide superconductor crystals. Furthermore, a semiconductor substrate having an insulating layer on its surface can also be used.

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 has a superconducting layer 1 formed on a substrate 5 having a protrusion 50. The superconducting element shown in FIG. The superconducting layer 1 is composed of a C-axis oriented oxide superconducting thin film, and the substrate 5 of the superconducting layer 1
The upper part of the protrusion 50 has a thickness of 5n+y+ or less and forms the superconducting channel 10. Further, on both sides of the superconducting channel 10 of the superconducting layer 1, the height is lowered by about 1Q nm, and a source electrode 2 and a drain electrode 3 made of a C-axis oriented oxide superconducting thin film are arranged.

Further, a gate electrode 4 is arranged on the superconducting channel 10 with an insulating film 6 interposed therebetween.

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, a protrusion is formed on the substrate 5 as shown in FIG. 2(a). As the substrate 5, M
Insulator substrates such as g0 (100) substrates, 5rTi03 (100) substrates, or 5i (100
) and the like are preferred. However, when a semiconductor substrate is used, an insulating film is formed on the surface after forming protrusions as described later.

Next, as shown in FIG. 2 et al., a part of the substrate 5 is covered with a photoresist 8, and the surface is etched by a dry etching method such as Ar ion etching to form a protrusion 50.

When using a semiconductor substrate, the crystal orientation is also important.
As mentioned above, the steps are slightly different. For example, 5i (100
) If a substrate is used, the photoresist 8 is formed so that the (110) plane is perpendicular to the 5i (100) plane in the gate longitudinal direction, that is, in the channel current flow direction. This Si substrate is etched using an etching solution such as KOH or APW to form protrusions 50. For example, MgAl is applied to the surface of this substrate by CVD method.
A 2O4 layer and a BaT i 03 layer are successively deposited by sputtering.

Next, a C-axis oriented oxide superconducting thin film is formed on the processed substrate 5 as shown in FIG. Then, a superconducting layer 1 is formed. As an oxide superconductor,
Y-Ba-Cu-0 based oxide superconductor, Bi-3r
-Ca -Cu -0 based oxide superconductor, Tl -Ba
-Ca-Cu-0 based oxide superconductor is preferred.

Y1Ba2Cu30i by offaxis battering method
The sputtering conditions for forming an oxide superconducting thin film with -xC axis orientation are shown below.

Sputtering gas Ar:90%02:1
0% Pressure 10 Pa Substrate temperature 700° C. The superconducting layer 1 is formed so that the thickness of the portion of the superconducting layer 1 above the protrusion 50 is 5 m or less. Next, Figure 2 (6)
As shown in FIG. 2, an insulating film 16 is formed on the superconducting layer 1. The insulating film 16 is preferably made of MgO, but it is also preferable to use other insulators that do not create a large level at the interface with the oxide superconducting thin film. Next, as shown in FIG. 2(e), the insulating film 1
A normal conductor film 17 is formed on 6. For the normal conductor film 17, it is preferable to use a high melting point metal such as Au or Ti5W, or a silicide thereof. From the viewpoint of suppressing interface states, preventing contamination, and reducing mechanical stress, it is desirable that the upper rudder insulating film 16 and normal conductor film 17 be formed continuously on the superconducting layer 1.

Next, a gate electrode pattern is formed using the heat-resistant mask film 9, and the gate electrode 4 and the insulating layer 6 are etched by reactive ion etching or Ar ion milling as shown in FIG. 2(f).
form. The heat-resistant mask film 9 can be made of a high-melting point metal such as Mo, and can be formed by vacuum evaporation or the like. If necessary, side etching is promoted to shorten the lengths of the gate electrode 4 and the insulating layer 6. After forming the gate electrode 4 and the insulating layer 6, as shown in FIG.

As shown in FIG. 2, a source electrode 2 and a drain electrode 3 are formed of a C-axis oriented thin film of the same oxide superconductor as the superconducting layer 1. The source electrode 2 and drain electrode 3 are formed to have a thickness of about 200 nm.

Any method can be selected as the film forming method, such as an oxidative sputtering method, a reactive vapor deposition method, an MBE method, or a CVD method.

Y 1Ba2Cu30 by ophaxis battering method
The sputtering conditions for forming a 7-X C-axis oriented oxide superconducting thin film are shown below.

Sputter link residue Ar:90%02:10
% Pressure 10 Pa Substrate temperature 640°C At the same time, the a-axis oriented oxide superconducting thin film 19 is deposited on the heat-resistant mask film 9, but if Mo is used as the heat-resistant mask film 9, it will sublimate during film formation and the The superconducting device of the present invention is completed as shown in FIG. 2(i). Alternatively, an insulating film may be used for the heat-resistant mask film 9 instead of a heat-resistant resist, and may be left on the gate electrode 4.

When the superconducting element of the present invention is manufactured by the method of the present invention, a current can be uniformly passed through the superconducting channel, and the superconducting FE
It is possible to improve the characteristics of T. Further, 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 the superconducting proximity effect is not used, restrictions on microfabrication technology are relaxed.

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...Superconducting layer, 2...3...Superconducting drain electrode, 4...Superconducting gate electrode, source electrode, ・Substrate

Claims (2)

[Claims] (1) A superconducting channel formed in an oxide superconducting thin film formed on a substrate, a source electrode and a drain electrode arranged near both ends of the superconducting channel to flow a current through the superconducting channel, and a source electrode and a drain electrode arranged on the superconducting channel. A superconducting element comprising a gate electrode disposed in a gate electrode for controlling a current flowing through the superconducting channel, wherein the substrate has a protrusion, the oxide superconducting thin film is composed of a c-axis oriented oxide superconductor crystal, Further, a portion above the protrusion is made thin, the thin portion of the oxide superconducting thin film is the superconducting channel, and the source electrode and the drain electrode are made of an a-axis oriented oxide superconductor crystal. A superconducting element characterized by: (2) In the method for manufacturing a superconducting element according to claim 1, on an insulating substrate on which a protrusion is formed or on a semiconductor substrate on which a protrusion is formed and has an insulating film on the surface,
forming a c-axis oriented oxide superconducting thin film with a thickness of 5 nm or less on the protrusion, etching portions of the c-axis oriented oxide superconducting thin film on both sides of the protrusion by 10 nm or more;
A method for manufacturing a superconducting element, comprising the step of forming an a-axis oriented oxide thin film on the etched portion.