JPH08236825A - Superconducting element and its forming method - Google Patents

Abstract

PURPOSE: To form an effective superconducting quantum thin wire in normal conductor forming a superconducting junction, by designing the width of a superconducting electrode to be narrower than an ordinary superconducting junction. CONSTITUTION: The width of superconducting electrodes 301, 302 is 1.0μm, and the electrode width of their tip parts is 0.5μm. The interval 200 between the superconducting electrodes 301 and 302 of superconducting junction parts where the superconducting electrodes face with each other via normal conductor is 0.5μm. In the state that a gate voltage is not applied, superconductivity couples in the normal conductor constituting the superconducting junction in a region which becomes shorter than the coherence length. The region becomes equivalent to a superconducting quantum wire. The width of the region where superconductivity couples in the normal conductor becomes much thinner than the width of an actual superconducting electrode, as the result of the influence of the boundary in the electrode width direction. When the width of the superconducting coupling region becomes narrower than the normal coherence length, an effective superconducting quantum wire can be formed in the normal conductor forming the superconducting junction.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a superconducting device and a method for manufacturing the same.

[0002]

2. Description of the Related Art Conventionally, a so-called three-terminal type superconducting element in which a gate electrode is provided on a planar type superconducting junction is known as The New Superconducting Electronics (NATO Advanced Study Institute Series, Crew). War Academic Publishers, 1993) pp. 249-275. These prior arts show the operating characteristics of a superconducting field effect type three-terminal element in which the normal conductor is a metal or a semiconductor.

[0003]

Among the conventional techniques,
The function that the superconducting element can fulfill is only a simple switching operation by controlling the superconducting current by applying a voltage to the gate electrode.

The object of the present invention is to realize a logical function with a single element at a very high speed and low power consumption according to a new operating principle.
Another object is to provide a functional superconducting device that facilitates parallel processing by combining these devices.

[0005]

In order to achieve the above object, the superconducting element of the present invention has a structure of a planar type superconducting junction in which a plurality of superconducting conductive electrodes are coupled via a normal conductor.
The region of the superconducting junction where superconductivity is combined in the normal conductor is the region of the first normal conductor where the superconducting electrode is close to the superconducting electrode due to the shape of the superconducting electrode, and the distance between the superconducting electrodes is greater than that. It is composed of superconducting electrodes having a shape such that at least one large second normal conductor region is formed, and it is possible to control the area of the superconducting junction in the second normal conductor region. The gate electrode is configured as follows.

[0006]

In the superconducting device of the present invention, the width of the superconducting electrode is designed to be narrower than that of an ordinary superconducting junction (typically 1 μm).
m or less). In the superconducting junction designed in this way, the width of the region where the superconductivity is coupled in the normal conductor becomes much smaller than the actual width of the superconducting electrode due to the influence of the boundary in the electrode width direction. When the width of the superconducting coupling region becomes narrower than the normal coherence length, in the normal conductor forming the superconducting junction,
An effective superconducting quantum wire is formed.

When the superconducting quantum wire is formed, the superconducting junction transits from the superconducting state to the voltage state by the quantum mechanical transition process of the phase difference of the superconducting waveguide function defined by the superconducting junction. This effect is called macroscopic quantum phase slip. Macroscopic quantum phase slip occurs at a bias current value below the critical current of a superconducting junction.

In the superconducting element according to the present invention, the region of the first normal conductor in which the superconducting electrodes are close to each other due to the shape of the superconducting electrodes and the region of the second normal conductor in which the distance between the superconducting electrodes is larger than that. And at least one each. With this device configuration, the transition to the voltage state due to macroscopic quantum phase slip becomes dominant and stable. Since the voltage state below the critical current is dominant and stable, the current-voltage characteristics of the superconducting device of the present invention have a negative resistance reflecting macroscopic quantum phase slip.

When the negative resistance due to the above-mentioned macroscopic quantum phase slip is used, the superconducting element according to the present invention is used for AN.
Logical functions such as D, OR, XOR and NAND can be executed. Further, when a voltage is applied to the gate electrode, the way in which the negative resistance of the current-voltage characteristic is generated changes. By utilizing this controllability, it is possible to realize a superconducting device that can execute a logic function by itself and can switch the logic function by applying a voltage to the gate electrode.

[0010]

【Example】

(Embodiment 1) FIG. 1 is a top view of a superconducting element according to a first embodiment of the present invention. FIG. 2 is a sectional view of the first embodiment of the present invention taken along the line CC 'in FIG. First, a basic manufacturing process of the superconducting element according to the present invention will be described with reference to FIG. A field oxide film 101 having a thickness of about 550 nm is formed on the surface of a substrate 100 made of silicon single crystal by a thermal oxidation method. Then, by implanting boron ions, a low impurity concentration region 102 in the semiconductor is formed.
Further, a multi-layer film for the gate electrode, which is made of polycrystalline silicon 103 and silicon nitride 104, is formed. The gate electrode multilayer film thus formed was processed by repeating the electron beam direct writing method and etching to form a gate electrode.
Then, arsenic ions are implanted to form the high impurity concentration region 105. By the above manufacturing process, a substrate having a gate electrode can be formed immediately above the impurity concentration region used as the normal conductor region.

The surface of this substrate is cleaned, and then a superconductor layer made of superconductor Nb and having a thickness of 100 nm is formed by a molecular beam method in a high vacuum. The superconducting layers 301 and 302 facing each other and the gate electrode 400 as shown in FIG. 1 are processed by the reactive ion etching method using the resist pattern formed by the electron beam direct writing method as a mask. A superconducting element containing the same can be obtained.

FIGS. 3 and 4 show current-voltage characteristics of the superconducting device according to the first embodiment of the present invention. 3 shows the case where the gate voltage is not applied, and FIG. 4 shows the case where the gate voltage is applied. When no gate voltage is applied, superconductivity is coupled in the normal conductor forming the superconducting junction in a region where the superconducting junction is shorter than the coherence length. This region is equivalent to a superconducting quantum wire. As a result, a macroscopic quantum phase slip that transitions from the superconducting state to the voltage state occurs due to the quantum mechanical process. In the superconducting device according to the present invention, the transition to the voltage state due to this phenomenon becomes dominant and stable. When the transition to the voltage state due to the macroscopic quantum phase slip becomes stable, a negative resistance occurs in the current-voltage characteristic. Further, when the gate voltage is applied, the width of the superconducting coupling region becomes wider. At this time, the transition to the voltage state due to the macroscopic quantum phase slip is suppressed and the negative resistance is weakened.

Next, the logical function operation based on the characteristic curves shown in FIGS. 3 and 4 will be described. In the present invention, consider the case where two independent inputs A and B are input to the superconducting electrode 301. At this time, each combination of the input signals shown in Table 1 and the corresponding current value are (0, 0) in FIGS.
It is indicated by symbols such as (0, 1).

When the gate voltage is not applied, there is a negative resistance due to the macroscopic quantum phase slip, so the input (0,
The response voltage for 0) is the largest. Therefore,
When the threshold voltage Vth as shown in FIG. 3 is set, the output is "1" only when the input is (0,0) and is "0". As a result, N shown in the truth table of Table 1
Can perform OR logic. Further, when a gate voltage is applied, the way in which negative resistance is generated is weakened. Therefore, when the input signal defined above is input, the voltage response of the superconducting element of the present invention is
The OR logic shown in Table 1 can be implemented.

[0015]

[Table 1]

Next, an example of processing dimensions of the superconducting element will be shown.
The width of the superconducting electrodes 301 and 302 shown in FIG. 1 is 1.0.
μm, and the electrode width at the tip portion thereof is 0.5 μm. The distance between the superconducting electrodes 301 and 302 in the superconducting junction where the superconducting electrodes are opposed to each other with the normal conductor interposed therebetween is 0.5 μm. This size is an example, and the size is not limited to this.
The recommended dimensions are 50 to 0 for the width of each superconducting electrode.
The distance between the first superconducting junctions where the superconducting electrodes face each other via the normal conductor is 50 to 0.05 μm, and the distance between the second superconducting junctions is 50 to 0.2 μm. A more desirable size is that the width of each superconducting electrode is 2
.About.0.5 .mu.m, and the size of the interval between the first and second superconducting junctions where the superconducting conductive electrodes face each other via the normal conductor is 0.5 to 0.1 .mu.m.

(Embodiment 2) FIG. 5 is a top view of a superconducting device according to a second embodiment of the present invention. The manufacturing process and materials used for the superconducting element of this embodiment may be the same as those of the first embodiment of the present invention. However, in this embodiment, the shape of the superconducting electrode is a convex needle electrode, and the gate electrode along the side surface of the tip of each superconducting electrode so that the superconducting junction is not affected by the electric field effect. The difference is that they are formed. Also in the case of this embodiment, as in the first embodiment, a region equivalent to the superconducting quantum wire is formed in the superconducting junction, and macroscopic quantum phase slip occurs. Since the superconducting pole is a convex needle electrode, the width of the region equivalent to the quantum wire becomes narrower, the transition to the voltage state due to the quantum phase slip becomes more dominant, and the negative resistance is generated first. It becomes more remarkable than the result shown in the first embodiment.

When a gate voltage is applied, the region where the superconductivity exudes only in the electrode width direction expands near the superconducting junction 201 shown in FIG. 5 due to the shape of the gate electrode. Therefore, the width of the effective superconducting quantum wire becomes wider, and the generation of negative resistance due to macroscopic quantum phase slip is suppressed, but the degree thereof is weaker than that of the first embodiment. This is because the electric field effect is not significantly generated in the superconducting junction due to the shape of the gate electrode, and the macroscopic quantum effect is not extremely suppressed.

FIGS. 6 and 7 show current-voltage characteristic diagrams of the superconducting device according to this embodiment. The meanings of the symbols used in the drawings are the same as in the case of the first embodiment (FIGS. 3 and 4). Also,
6 shows the case where the gate voltage is not applied, and FIG. 7 shows the case where the gate voltage is applied. Based on these current-voltage characteristics, as in the first embodiment of the present invention, XOR is applied when the gate voltage is not applied, and N is applied when the gate voltage is applied.
AND logic can be implemented. Table 2 shows each truth table.

[0020]

[Table 2]

(Embodiment 3) FIG. 8 is a top view of a superconducting device according to a third embodiment of the present invention. The manufacturing process and materials used for the superconducting device of this embodiment may be the same as those of the first embodiment of the present invention. However, this example is different in that one of the superconducting electrodes does not have a step structure and the gate electrode is also formed in a shape that completely covers the superconducting junction. As shown in the first and second embodiments of the present invention, it is possible to control how negative resistance is caused by macroscopic quantum phase slip depending on the shapes of superconducting and gate electrodes. As for the shapes of the superconducting electrode and the gate electrode in this embodiment, only the superconducting electrode 301 has a rectangular shape so that the peak of the negative resistance becomes broad.

9 and 10 show current-voltage characteristics of the superconducting device according to this embodiment. Further, FIG. 9 shows current-voltage characteristics when the gate voltage is not applied and FIG. 10 shows current-voltage characteristics when the gate voltage is applied. Based on these current-voltage characteristics, it is possible to execute OR when the gate voltage is not applied and AND logic when the gate voltage is applied, as described in the first embodiment. Table 3 shows each truth table.

[0023]

[Table 3]

(Embodiment 4) FIG. 11 is a top view of a superconducting device according to a fourth embodiment of the present invention. The manufacturing process and materials used for the superconducting element of this embodiment may be the same as those of the first embodiment. However, in this embodiment, one superconducting electrode used as an input is composed of two independent superconducting electrodes, and the structure of each superconducting junction is NAND (XOR) and OR (AND) shown in Examples 2 and 3, respectively. It has an element configuration that fulfills the logical function. Therefore, parallel processing of four logic functions can be executed depending on whether or not a voltage is applied to the gate electrodes 410 and 420. Table 4 summarizes the parallel processing executed depending on whether or not the gate voltage is applied.
Parallel processing can be performed by combining functional elements capable of switching logical functions as in the present embodiment.

[0025]

[Table 4]

The logical operation of the superconducting element shown in the first to fourth embodiments of the present invention can be obtained by cooling the superconducting element of the present invention in, for example, liquid helium. Further, although Nb is used as the superconductor in the above embodiments, Pb or an alloy of Pb, Nb may be used instead.
b intermetallic compound such as NbN, Nb Sn, NbG
You may use e, NbAl, NbSi etc. Although Si is used as the normal conductor, the object of the present invention can be achieved by using a semiconductor compound such as GaAs or InAs instead of Si.

In the above-mentioned fourth embodiment of the present invention, only the case where there are two superconducting conductive electrodes and gate electrodes connected to the superconducting junction portion to be processed in parallel is shown. A logic function superconducting device that executes parallel processing of many logic operations can be realized.

[0028]

According to the present invention, a plane type superconducting junction is used, and a region equivalent to a superconducting quantum wire is effectively formed in a normal conductor by superconducting bleeding. It enabled quantum phase slip to occur remarkably. Furthermore, by applying a voltage to the gate electrode, the region where the superconductivity exudes was expanded, and it became possible to realize a superconducting device that controls macroscopic quantum phase slip, which was not possible with conventional three-terminal superconducting devices.

When this superconducting element is used, logical operation functions (AND, OR, NAND, NO, which are realized by constructing a circuit using a plurality of switching elements).
(R, XOR) can be realized by a single element. Furthermore, by combining these elements, it is possible to realize a superconducting element capable of switching logical functions and executing parallel processing. By utilizing the features of the superconducting element according to the present invention, it is possible to realize a superconducting element and an information processing unit which are excellent in integration and have high speed and low power consumption.

[Brief description of drawings]

FIG. 1 is a top view of a superconducting device according to a first embodiment of the present invention.

FIG. 2 shows C- in FIG. 1 according to the first embodiment of the present invention.
Sectional drawing which shows C'section.

FIG. 3 is a current-voltage characteristic diagram showing operating characteristics of the superconducting element in the first embodiment of the present invention.

FIG. 4 is a current-voltage characteristic diagram showing operating characteristics of the superconducting element in the first embodiment of the present invention.

FIG. 5 is a top view of a superconducting device according to a second embodiment of the present invention.

FIG. 6 is a current-voltage characteristic diagram showing the operating characteristics of the superconducting element according to the second embodiment of the present invention.

FIG. 7 is a current-voltage characteristic diagram showing operating characteristics of the superconducting element according to the second embodiment of the present invention.

FIG. 8 is a top view of a superconducting device according to a third embodiment of the present invention.

FIG. 9 is a current-voltage characteristic diagram showing the operating characteristics of the superconducting element according to the third embodiment of the present invention.

FIG. 10 is a current-voltage characteristic diagram showing operating characteristics of the superconducting element in the fourth example of the present invention.

FIG. 11 is a top view of a superconducting device according to a fourth embodiment of the present invention.

[Explanation of symbols]

301, 302 ... Superconducting electrode (Nb), 400 ... Gate electrode, 200 ... Superconducting junction.

Claims (9)

[Claims] 1. A superconducting junction having a planar structure in which a plurality of superconducting electrodes are coupled via a normal conductor, and a region of the superconducting junction in which superconductivity is coupled in the normal conductor is the superconducting electrode. Of a first normal conductor having a superconducting electrode close to each other by a shape of and a region of a second normal conductor having a larger distance between the superconducting electrodes than that, at least one by one. A superconducting element comprising a superconducting electrode, wherein a gate electrode is constituted so that the area of the superconducting junction can be controlled in the region of the second normal conductor. 2. The area of the superconducting junction defined in the width direction of the superconducting conductive electrode, the distance between electrodes, or both directions can be controlled by applying a voltage to the gate electrode. A superconducting element comprising the superconducting conductive electrode and the gate electrode. 3. The superconducting electrode according to claim 1, wherein the superconducting electrode defining the superconducting junction has a rectangular shape, and the gate electrode has a shape matching the rectangular shape of the superconducting electrode and covering a part thereof. element. 4. The superconducting electrode according to claim 1, 2 or 3, wherein the superconducting conductive electrode has a rectangular shape for controlling the area of the superconducting junction, and a plurality of gate electrodes are formed so as to cover the superconducting junction. Superconducting element. 5. The superconducting conductive electrode according to claim 1, wherein one of the superconducting conductive electrodes forming the superconducting bonding part is composed of a plurality of independent superconducting conductive electrodes, and each of the superconducting bonding parts formed by the superconducting conductive electrodes is A superconducting device provided with a gate electrode. 6. A superconducting element according to claim 1, 2, 3, 4 or 5, comprising a waveguide or a conductor for irradiating said superconducting junction with microwaves of high frequency. 7. The method according to claim 1, 2, 3, 4 or 5,
A superconducting element comprising a waveguide or an optical fiber for guiding laser light to the superconducting junction. 8. The method according to claim 1, 2, 3, 4 or 5.
The superconductor is a material selected from lead, a lead alloy, niobium, and a niobium intermetallic compound, and the normal conductor is selected from gold, silver, copper, or aluminum and its alloys, semiconductors, semiconductor compounds, or their compounds. A superconducting element composed of at least one material. 9. A superconducting junction structure in which a plurality of superconducting electrodes are coupled via a normal conductor, and a region of the superconducting junction where superconductivity is coupled in the normal conductor is the superconducting electrode. Of a first normal conductor having a superconducting electrode close to each other by a shape of and a region of a second normal conductor having a larger distance between the superconducting electrodes than that, at least one by one. In a superconducting element composed of a superconducting electrode and having a gate electrode so that the area of the superconducting junction can be controlled in the region of the second normal conductor, at least the electron beam direct drawing method is used. A method of manufacturing a superconducting element, comprising the step of processing a superconducting thin film of a superconducting junction of the above-mentioned superconducting junction.