JPH0555648A - Superconducting element - Google Patents

Abstract

PURPOSE:To improve the crystalline state of a Y1Ba2Cu3O7-x oxide superconducting thin film by a Pr1Ba2Cu3O7-y layer and to increase a substantial current capacity of a superconducting channel. CONSTITUTION:The superconducting element comprises a Pr1Ba2Cu3O7-y layer 6 formed on an MgO board 10, a superconducting channel 20 disposed near the center of a Y1Ba2Cu3O7-x oxide superconducting thin film 2 formed on the layer 6, a gate electrode 6 disposed on the channel 20 through a gate insulating layer 9, and a superconducting source electrode 3 and a superconducting drain electrode 4 formed of Y1Ba2Cu3O7-x oxide superconductor disposed at both sides of the channel 20.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a superconducting device.
More specifically, the present invention relates to a superconducting field effect type three-terminal element whose channel is composed of an oxide superconductor.

[0002]

2. Description of the Related Art It is considered that an element utilizing the superconducting phenomenon is faster than a conventional semiconductor element, consumes less power, and can be dramatically improved in performance. In particular, by using an oxide superconductor, which has been studied in recent years, it is possible to manufacture a superconducting element that operates at a relatively high temperature. As a superconducting element, a Josephson element is well known. However, since the Josephson element is a two-terminal element, the circuit becomes complicated when trying to configure a logic circuit. Therefore, a three-terminal superconducting element is practically advantageous.

The three-terminal superconducting element utilizes a superconducting proximity effect that causes a superconducting current to flow in a semiconductor between superconducting electrodes that are arranged close to each other, and a superconducting field effect that controls the superconducting current flowing in a superconducting channel with a gate electrode. Mold elements are typical. Both elements are capable of separating input and output, are voltage-controlled elements, and have a common point in that they have a signal amplifying action. However, in order to obtain the superconducting proximity effect, the superconductor electrode must be arranged within a distance of several times the coherence length of the superconductor (several nm in the case of an oxide superconductor). Therefore, very precise processing is required. On the other hand, a superconducting element whose channel is a superconducting channel has a large current capacity and does not require microfabrication in which the superconducting conductive electrodes are arranged close to each other in manufacturing.

FIG. 2 shows a schematic view of an example of a superconducting field effect device having a superconducting channel. The superconducting field effect device 1 of FIG. 2 is composed of a superconducting channel 20 arranged near the central portion of the oxide superconducting thin film 2 arranged on the substrate 10 and an oxide superconducting member arranged near both ends of the superconducting channel 20. It comprises a superconducting source electrode 3 and a superconducting drain electrode 4 formed of a body, and a gate electrode 5 arranged on the superconducting channel 20 via a gate insulating layer 9. In this superconducting field effect device, the superconducting current flowing through the superconducting channel 20 between the superconducting source electrode 3 and the superconducting drain electrode 4 is controlled by the voltage applied to the gate electrode 5.

[0005]

In the above superconducting field effect element, since the superconducting current flowing in the superconducting channel 20 is controlled by the voltage applied to the gate electrode 5, the superconducting channel 20 and the gate insulating layer 9 have different thicknesses. Must be extremely small. Specifically, the superconducting channel 20
Is preferably 5 nm or less, about 5 unit cells of the oxide superconductor crystal, and the thickness of the gate insulating layer 9 is preferably sufficiently thin and about 10 nm at which tunnel current does not flow. .. However, in practice superconducting channels
When 20 is formed of an oxide superconducting thin film having a thickness of 5 unit cells of an oxide superconductor crystal, the upper and lower portions having a thickness of 1 to 2 unit cells may not show superconductivity, The current value that can be passed through the superconducting channel 20 was limited.

The reason why the lower portion of the superconducting channel 20 having a thickness of 1 to 2 unit cells does not exhibit superconductivity is that the substrate material and the oxide superconductor constituting the oxide superconducting thin film have different thermal expansion coefficients. Therefore, when the temperature reaches room temperature after the film formation, the crystal under the thin film is distorted. Further, it may be caused by the atoms constituting the substrate diffusing into the oxide superconductor crystal.

Therefore, an object of the present invention is to provide a superconducting field effect element in which the non-superconducting portion of the oxide superconducting thin film forming the above-mentioned superconducting channel is reduced.

[0008]

According to the present invention, a superconducting source region and a superconducting drain region formed of an oxide superconductor disposed on a substrate and disposed between the superconducting source region and the superconducting drain region. A superconducting channel composed of an oxide superconductor, and a normal conductor arranged on the superconducting channel via a gate insulator layer and to which a gate voltage is applied to control a current flowing through the superconducting channel. In a superconducting field effect device including a gate electrode, a Pr ₁ Ba ₂ film having a thickness substantially equal to that of the superconducting channel is provided between the superconducting channel and the substrate.
A superconducting device comprising a Cu ₃ O _7-y layer is provided.

[0009]

The superconducting device of the present invention is provided with a Pr ₁ Ba ₂ Cu ₃ layer having a thickness approximately equal to that of the superconducting channel between the substrate and the superconducting channel.
Its main feature is that it has a buffer layer composed of O _7-y . The superconducting channel formed on the Pr ₁ Ba ₂ Cu ₃ O _7-y layer improves the crystalline state of the oxide superconducting thin film that constitutes the superconducting channel, and the crystalline unit cell at the bottom of the oxide superconducting thin film is also in the superconducting state. become. This is Pr ₁ Ba ₂ Cu
_{Since the 3} O _7-y crystal has a layered structure similar to that of the oxide superconductor crystal and has good lattice matching with the oxide superconductor crystal, it is oxidized on the Pr ₁ Ba ₂ Cu ₃ O _7-y layer. It is believed that the formation of the superconducting thin film supplements the incomplete portion of the oxide superconductor crystal under the oxide superconducting thin film. Further, the strain due to the difference in the coefficient of thermal expansion from the substrate is also absorbed by the Pr ₁ Ba ₂ Cu ₃ O _7-y layer, and the diffusion of atoms from the substrate also stops only within the Pr ₁ Ba ₂ Cu ₃ O _7-y layer. .. Therefore, in the superconducting device of the present invention, Pr ₁ Ba ₂ Cu
_{The 3} O _7-y layer needs to have a thickness almost equal to that of the superconducting channel, and if it is thinner than that, the effect is not sufficient. Further, even if it is thicker than the superconducting channel, its effect remains the same.

In the superconducting device of the present invention, Pr ₁ Ba ₂ Cu is used.
The crystalline state of the ₃ O _7-y layer must be good. The MBE method is preferably used to form an extremely thin Pr ₁ Ba ₂ Cu ₃ O _7-y layer having a good crystal state. Especially RHE
It is preferable to grow the Pr ₁ Ba ₂ Cu ₃ O _7-y layer by the MBE method while monitoring it by ED (reflection high-energy electron diffraction) because the film thickness can be accurately controlled in a unit of monolayer. The oxide superconducting thin film that constitutes the superconducting channel is also MB
When the film is formed by the E method, it is possible to continuously form the oxide superconducting thin film after forming the Pr ₁ Ba ₂ Cu ₃ O _7-y layer.

The present invention can be applied to any oxide superconductor, but the Y ₁ Ba ₂ Cu ₃ O _{7 -X} oxide superconductor is preferred because it can stably obtain a high quality thin film with good crystallinity. .. Further, the Bi ₂ Sr ₂ Ca ₂ Cu ₃ O _x oxide superconductor is particularly preferable because its superconducting critical temperature Tc is high.

Hereinafter, the present invention will be described in more detail with reference to examples, but the following disclosure is merely examples of the present invention and does not limit the technical scope of the present invention.

[0013]

1 is a schematic sectional view showing an example of a superconducting element of the present invention. Superconductive elements of the present invention shown in FIG. 1, the _{Pr 1 Ba 2 Cu 3 O 7} -y layer 6 formed on the MgO substrate 10, Pr ₁ Ba ₂ Cu ₃
A superconducting channel 20 arranged near the center of the Y ₁ Ba ₂ Cu ₃ O _7-X oxide superconducting thin film 2 formed on the O _7-y layer 6;
A superconducting source composed of a gate electrode 5 arranged on the superconducting channel 20 via a gate insulating layer 9 and Y ₁ Ba ₂ Cu ₃ O _7-X oxide superconductors arranged on both sides of the superconducting channel 20. An electrode 3 and a superconducting drain electrode 4 are provided.

In the above superconducting device of the present invention, Pr ₁ Ba ₂ Cu _{3 is used.}
The O _7-y layer 6 is composed of a thin film of 5 unit cells of Pr ₁ Ba ₂ Cu ₃ O _7-y crystal with c-axis orientation, and its thickness is about 5 nm. The superconducting channel 20 was composed of an oxide superconducting thin film 2 in which 5 units of c-axis oriented Y ₁ Ba ₂ Cu ₃ O _7-X oxide superconducting crystals were laminated, and the thickness thereof was about 5 nm. On the other hand, the gate insulating layer 9 is made of MgO and has a thickness of about 10 nm.

A method for producing the superconducting element of the present invention will be described below. First, a Pr ₁ Ba ₂ Cu ₃ O _7-y crystal with 5 units of c-axis orientation was laminated on the MgO substrate 10 by the MBE method while monitoring by RHEED, and the Pr ₁ Ba ₂ Cu ₃ O _7-y layer 6 was formed. To form a film. Sequentially stacking 5 unit cells of c-axis oriented Y ₁ Ba ₂ Cu ₃ O _7-X oxide superconductor crystal on the Pr ₁ Ba ₂ Cu ₃ O _7-y layer 6,
₁ Ba ₂ Cu ₃ O _7-X oxide superconducting thin film 2 is formed. Y ₁ Ba ₂ Cu
_The gate insulating film 9 is formed of MgO at the center of the ₃ O _{7 -X} oxide superconducting thin film 2, and the gate electrode 5 is formed of Au on the gate insulating film 9. After that, Y ₁ Ba ₂ Cu ₃ O _7-X oxide superconducting thin film 2
A Y-axis oriented Y ₁ Ba ₂ Cu ₃ O _7-X oxide superconducting thin film is laminated on both ends of the superconducting source electrode 3 and the superconducting drain electrode 4 to complete the superconducting device of the present invention.

In the superconducting element of the present invention produced as described above, the crystal layer of at least 3 unit cells from the lower surface of the Y ₁ Ba ₂ Cu ₃ O _{7 -X} oxide superconducting thin film 2 showed superconducting property. Therefore, the cross-sectional area of the superconducting channel is substantially larger and the current capacity is larger than that of the conventional superconducting element.

[0017]

As described above, according to the present invention,
A superconducting three-terminal element having higher performance than ever before is provided. By applying the present invention to the production of superconducting circuits and electronic devices, it is possible to greatly improve the performance of electronic devices.

[Brief description of drawings]

FIG. 1 is a schematic sectional view of a superconducting field effect element of the present invention.

FIG. 2 is a schematic cross-sectional view of a conventional superconducting field effect element.

[Explanation of symbols]

 1 superconducting field effect device 2 oxide superconducting thin film 3 superconducting source electrode 4 superconducting drain electrode 5 gate electrode

Claims (1)

[Claims] 1. A superconducting source region and a superconducting drain region formed of an oxide superconductor arranged on a substrate, and a superconducting oxide superconductor arranged between the superconducting source region and the superconducting drain region. A superconducting field effect comprising a channel and a gate electrode formed on the superconducting channel via a gate insulator layer and composed of a normal conductor to which a gate voltage is applied to control a current flowing through the superconducting channel. A mold element, comprising a Pr ₁ Ba ₂ Cu ₃ O _7-y layer having a thickness substantially equal to that of the superconducting channel between the superconducting channel and the substrate.