JPH04116875A - Superconducting element and its manufacture - Google Patents

Abstract

PURPOSE:To unnecessitate fine work technique, stabilize element performance, and improve reliability, by a method wherein a thinned part on the protruding part of a substrate, of an oxide superconducting thin film formed on the substrate provided with the protruding part, is made a superconducting channel. CONSTITUTION:A protruding part is formed on a substrate 5; a part of the substrate 5 is covered with photo resist 8; the surface is shaved by a dry etching method, and a protruding part 50 is formed. An oxide superconducting film is formed on the substrate 5, and a superconducting layer 1 is formed. The surface of said layer 1 is flattened, and the upper part of the protruding part 50 of the substrate 5 is thinly worked as follows; the superconducting layer 1 is so coated with photo resist 9 that the surface becomes flat, and the superconducting layer 1 is flattened by ion etching or the like until the thickness of a superconducting channel 10 on the protruding part 50 becomes 5nm. Next an insulating film 6 and a metal film 7 are laminated on the superconducting layer 1. Said laminated films are eliminated by etching, in the manner in which only the part on the superconducting channel 10 is left, and a gate electrode 4 is formed. Finally a source electrode 2 and a drain electrode 3 are formed on both sides of the gate electrode 4, thereby completing an element.

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, since an oxide superconductor has a short coherence length, when an oxide superconductor is used, the distance between the superconducting source electrode 41 and the superconducting drain electrode 42 is several On+n.
It has to be moderate. 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 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 substrate has a protrusion above the protrusion of the oxide superconducting thin film. There is provided a superconducting element characterized in that a portion of the oxide superconducting thin film is made thin, and the thin portion of the oxide superconducting thin film is the superconducting channel.

Furthermore, in the present invention, as a method for manufacturing the above superconducting element, an oxide superconducting thin film is formed 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. However, there is provided a method for manufacturing a superconducting element characterized by including a step of flattening the surface of the thin film.

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 on the order of 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 superconducting element of the present invention, a portion of an oxide superconducting thin film formed on a substrate provided with a protrusion, which becomes thinner due to 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;

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 crystals.

Further, the superconducting element of the present invention includes a Y-Ba-CuO-based oxide superconductor, a Bi-3r-Ca-Cu-0-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 having a flat surface formed on a substrate 5 having a protrusion 50. The superconducting element shown in FIG.

The portion of the superconducting layer 10 above the protrusion 50 of the substrate 5 is thinned to form a superconducting channel 10 . A gate electrode 4 is arranged on the superconducting channel 10 and the superconducting layer 1
On both sides of the upper superconducting channel 10, a source electrode 2 and a drain electrode 3 are arranged.

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
An insulating substrate such as a g0 (100) substrate or a 5rT103 (100) substrate, or a semiconductor substrate such as 81 having an insulating film on the surface is preferable. However, when a semiconductor substrate is used, an insulating film is formed on the surface after forming the protrusion.

Next, as shown in FIG. 2 (Corporation), a portion of the substrate 5 is covered with a photoresist 8, and the surface is etched using 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, when using a Si substrate, the photoresist 8 is formed so that the (110) plane is perpendicular to the gate longitudinal direction, that is, the channel current flow direction, with respect to the 5i (100) plane. This 81 substrate is etched using an etching solution such as KOH or APW to form the protrusion 50. The surface of this substrate is coated with l! gA10* and Bat+03 are successively laminated using a sputtering method.

Next, an oxide superconducting thin film is formed on the processed substrate 5 as shown in FIG. form 1. As the oxide superconductor, Y-Ba-
Cu-0 based oxide superconductor, B1-3r-Ca-Cu
A -0-based oxide superconductor and a TI-BaCa-Cu-0 based oxide superconductor are preferred, and a C-axis oriented thin film is preferred. This means that the C-axis oriented oxide superconducting thin film is
This is because the critical current density in the direction parallel to the substrate is large.

Since all parts of the superconducting layer 1 have a substantially constant thickness as it is, the surface is made flat and the part above the protrusion 50 of the substrate 5 is processed to be thin. For this purpose, as shown in FIG. 2(di), a photoresist 9 is coated on the superconducting layer 1 so that the surface is flat.Then, as shown in FIG. 10 thickness is 5nm
The superconducting layer 1 is made flat by ion etching or the like until it becomes ^r.

Next, a gate electrode is fabricated on the superconducting channel 10.

The gate electrode preferably has a structure in which a metal layer is laminated on an insulator layer. Therefore, as shown in FIG. 2(f), an insulating film 6 and a metal film 7 are laminated on the superconducting layer 1. For the insulating film 6, it is preferable to use an insulator that does not create a large level at the interface with the oxide superconducting thin film, such as MgO, and for the metal film 7, use a high melting point metal such as Au, TI, or W, or a silicide thereof. It is preferable. This stacked film is removed by etching leaving only the portion above the superconducting channel 10, as shown in FIG. 2 (gl), to form the gate electrode 4.

Finally, the source electrode 2 and drain electrode 3 are formed on both sides of the gate electrode 40, again using ^U, to complete the superconducting element of the present invention.

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. Schematic diagram of the base transistor, ! 4t! 1 is a schematic diagram of a superconducting FET. [Main reference numbers] 1... superconducting layer, 2... source electrode, 3... drain electrode,

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. In the superconducting element comprising a gate electrode disposed in the superconducting channel for controlling a current flowing through the superconducting channel, the substrate has a protrusion, a portion of the oxide superconducting thin film above the protrusion is thinned, and the substrate has a protrusion. A superconducting element, wherein the thin portion of the oxide superconducting thin film is the superconducting channel. (2) In the method for producing a superconducting element according to claim 1, an oxide superconducting thin film is formed 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 its surface. 1. A method for producing a superconducting element, comprising the steps of forming a thin film and flattening the surface of the thin film.