JPH05114757A - Superconductive element and manufacture thereof - Google Patents

Abstract

PURPOSE:To improve a superconductive electric field effect element in characteristics by a method wherein a non-superconductive oxide which constitutes a resistive channel is formed of oxide superconductor which has lost superconductive properties. CONSTITUTION:A superconductive electric field effect element 1, which is provided with a superconductive channel 2 arranged between a source region 13 and a drain region 14, and a resistive element 16, which is connected in parallel with the superconductive channel 2 between a source electrode 3 and a drain electrode 4 of the superconductive field effect element 1, are integrated together. The superconductive channel 2 and a resistive channel 6 of the resistive element 16 are electrically insulated from each other and formed of a thin film in one piece. The thin film concerned is made of oxide which forms the superconductive channel 2 and oxide superconductor which forms the resistive channel 6 having lost its superconductive properties due to the addition of impurities or due to lack of oxygen contained in crystal. By this setup, the superconductive electric field effect element 1 can be improved in characteristics.

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, it relates to a superconducting element in which a field effect type three-terminal element having a channel made of an oxide superconductor and a resistance element are integrated.

[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, but 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 the semiconductor between the superconducting electrodes arranged close to each other, and one that controls the superconducting current flowing in the superconducting channel with a gate electrode. It is 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 density and does not require microfabrication in which the superconducting conductive electrodes are arranged close to each other in manufacturing.

FIG. 4 shows a schematic view of an example of a superconducting field effect element having a superconducting channel. The superconducting field effect device 1 of FIG. 4 comprises a superconducting channel 2 made of an oxide superconductor arranged on a substrate 10, a source electrode 3 and a drain electrode 4 arranged near both ends of the superconducting channel 2, and a superconducting channel. 2 and a gate electrode 5 disposed on the gate insulating layer 9 via a gate insulating layer 9. In this superconducting field effect element, the superconducting current flowing between the source electrode 3 and the drain electrode 4 is controlled by the voltage applied to the gate electrode 5.

[0005]

The characteristics of the above-mentioned superconducting field effect element are shown in FIG. FIG. 5A is a graph showing the voltage-current characteristics between the source and the drain with respect to a specific gate voltage value in the superconducting field effect device shown in FIG. The characteristics shown in the graph of FIG. 5A are characteristics in an ideal state, which is so-called required characteristics. However, when an element having the required characteristics shown in FIG. 5A is actually operated, the characteristics shown in FIG. 5A are not exhibited, but the hysteresis characteristics are exhibited. FIG. 5B shows a change in current when the gate voltage of the superconducting field effect device having the characteristics shown in FIG. 5A is kept constant and the voltage between the source and the drain is changed.

As shown in FIG. 5 (b), in this superconducting field effect device, the current value changes differently when the voltage rises and when the voltage falls. In such a superconducting field effect device, the value of the source-drain current with respect to the value of the gate voltage and the value of the source-drain voltage is
Practicality is low because it cannot be specified.

Therefore, an object of the present invention is to provide a superconducting element with improved characteristics of the above-mentioned superconducting field effect element.

[0008]

According to the present invention, a superconducting channel composed of a source region and a drain region composed of an oxide superconductor and an oxide superconductor arranged between the source region and the drain region. And a superconducting field effect element including a gate electrode to which a gate voltage for controlling a current flowing through the superconducting channel is applied, and the superconducting field effect element is connected between the source region and the drain region, The superconducting part of the superconducting field effect element, and the resistance channel are integrated into a thin film, comprising a resistance channel composed of a non-superconducting oxide containing the same constituent element as the oxide superconductor forming the superconducting channel. The non-superconducting oxide, which is configured and constitutes the resistance channel, contains the impurities and loses the superconducting property. Superconducting device is provided, characterized in that less oxygen in is composed of the oxide superconductor loses superconductivity.

Further, in the present invention, in a method for producing a superconducting element having a superconducting region made of an oxide superconductor and a resistance region made of a non-superconducting oxide, a superconducting region of the superconducting element and Forming an oxide superconducting thin film having an area larger than the resistance region, and implanting impurity ions into a portion to be the resistance region of the oxide superconducting thin film, or of a portion to be the resistance region of the oxide superconducting thin film. Provided is a method for producing a superconducting element, which comprises reducing oxygen in an oxide superconductor crystal to convert an oxide superconductor into a non-superconducting oxide.

[0010]

The superconducting element of the present invention comprises a superconducting field effect element having a superconducting channel arranged between a source region and a drain region, and a superconducting channel in parallel between the source region and the drain region of the superconducting field effect element. The connected resistance element is an integrated element, and the superconducting portion of the superconducting field effect element and the resistance channel of the resistance element are formed of an integrated thin film. In this thin film, the superconducting portion is composed of an oxide superconductor, and the resistance channel is an oxide superconductor that has lost superconductivity due to the addition of impurities.
Alternatively, it is composed of an oxide superconductor which has lost superconductivity due to too little oxygen in the crystal. Further, it is preferable that the superconducting channel and the resistance channel are electrically insulated from each other by an insulating region.

In other words, the superconducting portion and the resistance channel portion of the superconducting element of the present invention are formed of a single oxide superconducting thin film, and the resistance channel portion is doped with impurities in the oxide superconducting thin film. The non-superconducting oxide formed by the above process or the non-superconducting oxide formed by removing oxygen from the oxide superconducting thin film. The superconducting property of the oxide superconductor is highly sensitive to its composition, and the superconducting property is easily lost when impurities are added or the amount of oxygen in the crystal is small. Therefore, in the method of the present invention, impurities are added or oxygen is removed to change a part of the oxide superconductor forming the oxide superconducting thin film into the oxide of the resistor. The resistivity of the non-superconducting oxide is changed by adjusting the concentration of impurities to be added and the amount of oxygen to be removed.

In the method of the present invention, the method of adding impurities to a part of the oxide superconducting thin film is preferably an ion implantation method. Specifically, Ba ions, Ni ions, etc. are implanted. It is preferable that about 10 ¹⁶ ions / cm ² of ions are implanted while measuring the resistance value, and the acceleration voltage at the time of implantation is 40 to 150 kV.
It does not have any conductivity when implanted with an amount of ions exceeding the above range. On the other hand, the acceleration voltage of ions at the time of implantation is
If it is lower than the above range, ions are not implanted to a sufficient depth, and the effect of ion implantation is not obtained. Further, when ions are implanted at an acceleration voltage exceeding the above range, the surface of the oxide superconducting thin film is roughened and the characteristics are deteriorated.

On the other hand, in the method of the present invention, oxygen is removed from a part of the oxide superconducting thin film by performing heat treatment in a high vacuum. When the oxide superconductor is heated in an atmosphere having a low oxygen partial pressure, oxygen in the crystal is released and the amount of oxygen is reduced. The amount of oxygen removed can be changed depending on the treatment time, and the resistivity can be adjusted. Since the oxide superconductor has a large diffusion coefficient of oxygen in the direction perpendicular to the c-axis of the crystal (oxygen easily moves in the direction perpendicular to the c-axis), the above oxide superconducting thin film is c-axis oriented oxide superconductor. It is also preferable that the structure is made of crystal and processed into a shape in which oxygen escapes from the side surface of the portion that becomes the resistance channel. When the above heat treatment is performed, it is preferable to finally exhaust the gas to about 1 × 10 ⁻¹⁰ Torr, and the heating temperature is 380 to 500 ° C. in the case of the Y—Ba—Cu—O oxide superconductor. preferable. This is because in the Y-Ba-Cu-O-based oxide superconductor, oxygen in the crystal is most likely to move at about 400 ° C.

In the superconducting element of the present invention, the superconducting channel opened and closed by the gate electrode and the resistance channel are arranged in parallel between the source electrode and the drain electrode. Therefore, when the gate of the superconducting channel is closed, the resistance is reduced. A source-drain current flows through the channel. Therefore, the hysteresis characteristic peculiar to the superconducting field effect element is eliminated. Therefore, in the superconducting element of the present invention, the resistance value of the resistance channel should be a value considerably smaller than the resistance value between the source and drain of the superconducting channel when the gate of the superconducting channel of the superconducting field effect element is closed. I have to.

The present invention can be applied to any oxide superconductor, but a 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 by way of examples, but the following disclosure is merely examples of the present invention and does not limit the technical scope of the present invention.

[0017]

EXAMPLES FIGS. 1A and 1B are schematic views showing an example of a superconducting element of the present invention. 1 (a) is a plan view, and FIG. 1 (b) is a sectional view taken along the line AA in FIG. 1 (a). Figure 1 (a) and
The superconducting element of the present invention shown in (b) has a superconducting channel 2 composed of a Y ₁ Ba ₂ Cu ₃ O _7-X oxide superconductor forming a part of a thin film 11 formed on an MgO substrate 10. , A gate electrode 5 arranged on the superconducting channel 2, and a source region 13 and a drain region 14 arranged on both sides of the gate electrode 5 on the superconducting channel 2, respectively.
₁ Ba ₂ Cu ₃ O _7-X A superconducting source electrode 3 and a superconducting drain electrode 4 made of an oxide superconductor. The superconducting channel 2, superconducting source electrode 3, superconducting drain electrode 4 and gate electrode 5 form a superconducting field effect element.

Further, the thin film 11 on the MgO substrate 10 electrically insulates the resistance channel 6 arranged in parallel with the superconducting channel 2 and the both arranged between the superconducting channel 2 and the resistance channel 6. And an insulating region 7. A source electrode 3 and a drain electrode 4 are arranged near both ends of the resistance channel 6.

As mentioned above, the superconducting channel 2,
The resistance channel 6 and the insulating region 7 respectively form a part of the thin film 11 formed on the substrate 10. That is, a part of the thin film 11 is a superconductor, another part is a resistor, and another part is an insulator.
The resistance channel 6 and the insulating region 7 are formed.

A method for producing the superconducting element of the present invention will be described below. First, a pattern of the insulating region 7 is formed of SiO ₂ on the MgO substrate 10, and a Y ₁ Ba ₂ Cu ₃ O _7-X oxide superconducting thin film is formed thereon. The Y ₁ Ba ₂ Cu ₃ O _7-X oxide superconducting thin film can be formed by various sputtering methods, M
Any method such as a BE method, a vacuum vapor deposition method, a CVD method can be used. The main film forming conditions for forming a film by the sputtering method are shown below. Substrate temperature 700 ℃ Sputtering gas Ar 90% O ₂ 10% Pressure 5 × 10 ^-2 Torr Film thickness 400nm

During the growth of the above Y ₁ Ba ₂ Cu ₃ O _7-X oxide superconducting thin film, Si diffuses from the SiO ₂ layer on the MgO substrate 10 into the thin film and the insulating region 7 is automatically formed. To be done. After the Y ₁ Ba ₂ Cu ₃ O _7-X oxide superconducting thin film having the insulating region 7 is formed, the resistance channel 6 is formed in the Y ₁ Ba ₂ Cu ₃ O _7-X oxide superconducting thin film. The resistance channel 6 is formed by injecting impurity ions into a predetermined position of the Y ₁ Ba ₂ Cu ₃ O _7-X oxide superconducting thin film or by performing heat treatment to the Y ₁ Ba ₂ Cu ₃ O _{7-X at} that position.
It is formed by removing oxygen in the oxide superconductor crystal to the extent that it does not become an insulator. The conditions for ion implantation are shown below. Implanted ions Ba acceleration voltage 150 kV Implantation amount (dose amount) 10 ¹⁶ / cm ² The heat treatment conditions are shown below. Substrate temperature 450 ° C. Pressure 1 × 10 ^-10 Torr Treatment time 4 minutes The resistivity of the resistance channel 6 thus formed is the number of resistances of the superconducting channel 2 which is not in the superconducting state (when the gate is closed). Doubled.

When the insulating region 7 and the resistance channel 6 are formed as described above, the Y ₁ Ba ₂ Cu ₃ O _7-X oxide superconducting thin film includes the superconducting channel 2, the resistance channel 6 and the insulating region 7. It becomes the thin film 11. Y ₁ Ba ₂ Cu ₃ is also formed on both ends of the thin film 11 on the superconducting channel 2 and the resistance channel 6.
The superconducting electrodes 3 and 4 of the thin film of O _{7 -X} oxide superconductor are respectively formed and arranged. Also, on the superconducting channel 2
The superconducting element of the present invention is completed by forming the gate electrode 5 apart from the superconducting conductive electrodes 3 and 4 with a noble metal such as Au or Ag.

The operation of the superconducting element of the present invention will be described with reference to FIGS. 2 (a) and 2 (b) and FIG. 3 (c). 2 (a) and 2 (b) show the operation of the superconducting element of the present invention by an equivalent circuit. That is, the superconducting element of the present invention comprises a superconducting field effect element 1 and a source electrode 3 and a drain electrode 4 in parallel with a superconducting channel 2 of the superconducting field effect element 1.
It is equivalent to a circuit composed of a resistance element 16 connected between them. FIG. 2A shows a state in which, in the superconducting element of the present invention, no voltage is applied to the gate electrode 5 of the superconducting field effect element 1 and the gate of the superconducting channel 2 is open. At this time, since the superconducting channel 2 is in the superconducting state and the electric resistance is practically 0, all the source-drain current flows through the superconducting channel 2.

FIG. 2 (b) shows a superconducting device of the present invention.
A state is shown in which a voltage is applied to the gate electrode 5 of the superconducting field effect element 1 and the gate of the superconducting channel 2 is closed. In this case, the superconducting state of the superconducting channel 2 is lost. At this time, the resistance value R _s of the superconducting channel 2 is
The voltage between the source and drain rises and the superconducting channel 2
And the resistance value R _{down at the} moment when the current flowing in the superconducting channel 2 is cut off because the resistance value R _up when the current starts to flow and the voltage between the source and the drain drop. There is. R _up <R _s <R _{down The} resistance element 16 has a sufficient width and thickness for the superconducting channel 2, and its resistance value R is set to R << R _up. Most of the source-drain current flows through the resistance element 16. Therefore, the source-drain resistance in this case is approximately equal to R.

FIG. 3 (c) is a characteristic diagram of the superconducting element of the present invention. As shown in FIG. 3 (c), in the superconducting element of the present invention, the hysteresis characteristic of the superconducting field effect element 1 is significantly improved, and the uniqueness of the voltage-current characteristic between the source and the drain is improved by the gate voltage. be able to.
Therefore, the superconducting element of the present invention is highly practical, especially when used in electronic devices and the like.

[0026]

As described above, according to the present invention,
A highly practical superconducting three-terminal element is provided. By applying the present invention to the production of superconducting circuits and electronic equipment, it is possible to produce high-performance electronic devices that have never been obtained.

[Brief description of drawings]

FIG. 1 is a schematic view of a superconducting element of the present invention. (a) shows a plan view and (b) shows a sectional view taken along line (a) AA.

2 (a) and 2 (b) are conceptual diagrams showing the operation of the superconducting element of the present invention.

FIG. 3 (c) is a characteristic diagram of the superconducting element of the present invention.

FIG. 4 is a schematic view of a superconducting field effect device.

FIG. 5 is a characteristic diagram of a superconducting field effect device.

[Explanation of symbols]

 1 superconducting field effect device 2 superconducting channel 3 source electrode 4 drain electrode 5 gate electrode 6 resistance channel

Claims (2)

[Claims] 1. A source region and a drain region made of an oxide superconductor, a superconducting channel made of an oxide superconductor arranged between the source region and the drain region, and a current flowing through the superconducting channel. A superconducting field effect element having a gate electrode to which a gate voltage for controlling is applied, and an oxide superconductor connected between the source region and the drain region of the superconducting field effect element to form the superconducting channel. And a resistance channel formed of a non-superconducting oxide containing a constituent element equal to the superconducting portion of the superconducting field effect element, and the resistance channel is formed of an integrated thin film to form the resistance channel. The non-superconducting oxide has a low superconducting property due to a small amount of oxygen in the oxide superconductor or crystal that has lost the superconducting property due to inclusion of impurities Superconductive element characterized in that it is composed of the oxide superconductor Tsu. 2. A method for producing a superconducting device having a superconducting region made of an oxide superconductor and a resistance region made of a non-superconducting oxide, the size of the superconducting region being larger than the superconducting region and the resistance region of the superconducting device. Forming an oxide superconducting thin film having an area of 10 μm and implanting impurity ions into the resistance region of the oxide superconducting thin film, or an oxide superconductor crystal of the part forming the resistance region of the oxide superconducting thin film. A method for producing a superconducting element, characterized in that oxygen in the oxide is reduced to change an oxide superconductor to a non-superconducting oxide.