JPH0834322B2 - Superconducting element - Google Patents

Description

Detailed Description of the Invention

[Industrial applications]

The present invention is a Josephson junction device, a superconducting transistor, a superconducting switching device, etc., which utilizes the superconducting phenomenon.
The present invention relates to the field of superconducting electronics, and more particularly to the structures of oxide superconducting elements and oxide superconducting wirings, and the manufacturing method thereof.

[Prior art]

Josephson junction element, superconducting transistor, superconducting
Superconducting elements such as SQUID elements have excellent features such as ultra-high speed operation, low power consumption, and highly sensitive magnetic field detection. However, in the past, the superconducting phenomenon appeared only at an extremely low temperature near the temperature of liquid helium, and it was considered difficult to put it into practical use. However, recently discovered oxide superconductors have a critical temperature above the liquid nitrogen temperature, and the practical application of superconductors is making great progress. A superconducting field effect element is shown below as an example of the superconducting element. FIG. 1 shows a cross-sectional structure of a superconducting field effect element. Two sets of elements are depicted in FIG. The operating principle of the superconducting field effect device will be briefly described by using the superconducting proximity effect. By using the proximity superconducting proximity effect, a superconducting current flows from the source electrodes 1a, 1b made of a superconductor to the drain electrodes 2a, 2b also made of a superconductor through the semiconductor 3. Insulator 4
It is controlled by the gate voltage applied to the gate electrodes 5a and 5b attached via a and 4b. However, the theory indicates that when an oxide is used, the distance that the superconducting conductor spreads from the superconductor to the semiconductor (normal conductor) is extremely small. Therefore, it has been considered necessary to set the distance between the source and drain electrodes to 0.1 μm or less in the superconducting field effect device. However, the inventors have shown that these oxide superconductors exude a superconducting current due to the superconducting proximity effect over a longer distance than expected from conventional theory. The similarities are described in the 9th New Functional Device Technology Symposium Proceedings, pp. 85-90, 1990. However, it was only the laminated structure described, and it was unknown about the planar type. The inventors have found that even in a planar type superconducting element, the distance over which the superconducting conductor spreads in the semiconductor due to the proximity effect is longer than the conventional theoretical value. The fact that the superconducting proximity effect reaches a long distance means that the distance between the source and the drain can be made large, which facilitates the fabrication of the device including the formation of the gate electrode.

[Problems to be Solved by the Invention]

In the prior art, the fact that the superconducting proximity effect reaches a long distance means that the distance between the source and the drain can be made large, which facilitates the fabrication of the device including the formation of the gate electrode. However, the fact that the superconducting proximity effect reaches a long distance means that when the superconducting elements are integrated at high density and the distance between the superconducting elements or between the superconducting wires becomes short, the superconducting proximity effect also occurs between the superconducting elements and between the superconducting wires. Cause interaction with the device, causing malfunction of the device and increase of noise. For example, the superconducting current due to the superconducting proximity effect flows between the drain electrode 2a and the source electrode 1b in FIG. An object of the present invention is to suppress interaction between superconducting elements or between superconducting wirings due to the superconducting proximity effect, and to provide a specific method thereof.

[Means for Solving the Problems]

In order to achieve the above object, the superconducting element of the present invention can be solved by electrically isolating the superconducting element or the superconducting wiring so as not to affect each other. For example, as shown in FIG. 2, the above problem can be solved by etching and removing the semiconductor 3 between the drain electrode 2a and the source electrode 1b. As a method other than etching, there may be mentioned a method of preventing a superconducting current from flowing through the semiconductor 3 by using ion implantation or a chemical reaction, or a method of not forming a semiconductor between superconducting elements or between superconducting wirings from the beginning. .

[Action]

In the superconducting element of the present invention, by electrically isolating the superconducting elements or the superconducting wirings from each other, it is possible to prevent unnecessary interaction between the superconducting elements or between the superconducting wirings, and to achieve high integration of the superconducting elements. Is possible.

【Example】

Next, the present invention will be described in detail with reference to examples. FIG. 3 and FIG. 4 are a sectional structural view and a plan structural view of the produced superconducting field effect device. Ho as a superconductor
Ba ₂ Cu ₃ Ox (6.5 <x <7.0) is used and La _1.5 B is used as a semiconductor.
A planar type superconducting field effect device was manufactured using a _1.5 Cu ₃ Ox (6.5 <x <7.0). Substrate is SrTiO ₃ (110)
A single crystal substrate 12 was used. First, a La _1.5 Ba _1.5 Cu ₃ Ox (6.5 <x <7.0) semiconductor thin film 11 was formed on a substrate by the RF magnetron sputtering method. La _1.5 Ba _1.5 Cu _4.5 Ox for target
Was used. Substrate temperature is 650 ℃, sputter gas is 3
Ar-50% O _{2 at 0} mTorr, RF power 120 W, deposition rate 0.15 μm /
h, and the film thickness was 0.6 μm. After the film formation, it is cooled to room temperature in oxygen at 1 atm. Next, a HoBa ₂ Cu ₃ Ox (6.5 <x <7.0) superconducting thin film was formed thereon by a reactive vapor deposition method using microwave oxygen plasma. The substrate was heated to 580 ° C in oxygen plasma with an oxygen pressure of 8 × 1/105 Torr and a microwave power of 120 W, and plasma irradiation was performed for 30 minutes to remove surface stains. , Cu metal is evaporated so that the composition ratio becomes Ho: Ba: Cu = 1: 2: 3, and La _1.5 Ba _1.5 Cu ₃ Ox (6.5
A HoBa ₂ Cu ₃ Ox (6.5 <x <7.0) thin film was epitaxially grown on the <x <7.0) thin film. The film forming speed was 60 nm / h and the film thickness was 80 nm. After the film formation, it is cooled to room temperature in oxygen at 1 atm. La _1.5 Ba _1.5 Cu ₃ Ox (6.5 <x <
7.0) A pattern containing HoBa ₂ Cu ₃ Ox (6.5 <x <7.0) thin film on the semiconductor thin film including source electrodes 8a, 8b and drain electrodes 10a, 10b by reactive ion beam etching using SF6 gas It was made. HoBa ₂ Cu ₃ Ox (6.
5 <x <7.0) The gap between the thin films was 100 nm. On top of this, the insulating film SrTiO ₃ thin films 7a, 7b and HoBa ₂ C for the gate electrodes 9a, 9b are formed.
A u ₃ Ox (6.5 <x <7.0) thin film was formed. The respective film thicknesses were 150 nm and 100 nm. After film formation, HoBa ₂ Cu ₃ Ox (6.5 <
A pattern as the gate electrodes 9a and 9b was processed and molded on the x <7.0) thin film. Through the above steps, the superconducting field effect element shown in FIGS. 3 and 4 is manufactured. FIG. 5 shows the characteristics of the superconducting field effect device shown in FIG. When 3 V voltage was applied to the gate electrode 9, the superconducting current flowed 10 mA, and when no voltage was applied to the gate electrode 9, that is, in the off state, the superconducting current decreased to 1 mA. However, it was found that the current in the off state was large and did not operate sufficiently as an element. Example 1 After manufacturing up to the same steps as the structure of FIG. 4, La _1.5 Ba _1.5 Cu ₃ Ox (6.5 <x <7.
0) The semiconductor thin film was removed by etching to produce the structure shown in FIG. FIG. 7 shows the characteristics of the superconducting field effect element in this case. When the gate voltage is 0 V, that is, the superconducting current in the off state is 0.01 mA or less, and sufficient characteristics as an element can be obtained. As a result, it is possible to fabricate a superconducting circuit such as a logic circuit or a memory circuit in which a superconducting field effect element using an oxide superconductor, a superconducting wiring, a superconducting loop and the like are combined at intervals of 1 μm or less. Example 2 After manufacturing up to the same steps as the structure of FIG. 4, La _1.5 Ba _1.5 Cu ₃ Ox (6.5 <x <7.
0) Iron (Fe) ions were implanted into the semiconductor thin film at a rate of 10 ¹⁸ per cm 2 to fabricate the structure shown in Fig. 8. In this case as well, the same value as the characteristic of the first embodiment can be obtained, and even when this step is used, the superconducting field effect element using the oxide superconductor, the superconducting wiring, the superconducting loop, etc. are spaced at intervals of 1 μm or less. A superconducting circuit such as a logic circuit or a memory circuit combined in step 1 can be manufactured. Example 3 After manufacturing up to the same steps as the structure of FIG. 4, La _1.5 Ba _1.5 Cu ₃ Ox (6.5 <x <7.
0) Si was vapor-deposited on the semiconductor thin film. After vapor deposition, heat treatment is performed in oxygen at 500 ° C for 5 hours to convert Si into La _1.5 Ba _1.5 Cu ₃ Ox (6.5 <x <
7.0) Diffused in semiconductor thin film. When the characteristics of the superconducting field effect device manufactured in this way were measured, the same values as the characteristics of Example 1 could be obtained. In addition, by combining the superconducting field effect device, the superconducting wiring, the superconducting loop, etc., which are manufactured by using this process, at intervals of 1 μm or less, a superconducting circuit such as a logic circuit or a memory circuit can be manufactured.

【The invention's effect】

According to the present invention, a superconducting circuit including a superconducting field effect element using an oxide superconductor, a Josephson junction element, superconducting wiring, etc. can be highly integrated.

[Brief description of drawings]

Figure 1 shows the cross-sectional structure of a superconducting field effect device. FIG. 2 is a sectional structure of a superconducting field effect device using the present invention. FIG. 3 is a sectional structural view of the produced superconducting field effect element. FIG. 4 is a plan structure view of the produced superconducting field effect element. FIG. 5 shows current-voltage characteristics of the superconducting field effect device shown in FIGS. 3 and 4. (A) and (b) correspond to gate voltages of 3V and 0V, respectively. FIG. 6 is a plan structure view of the superconducting field effect element manufactured in Example 1. FIG. 7 shows the current of the superconducting field effect device shown in FIG.
Voltage characteristics. (A), (b) are gate voltage 3V, 0V respectively
It corresponds to. FIG. 8 is a plan structure view of the superconducting field effect device manufactured in Example 2. Explanation of symbols 1a, 1b …… source electrode, 2a, 2b …… drain electrode, 3 …… semiconductor, 4a, 4b …… insulator, 5a, 5b …… gate electrode, 6 …… substrate, 7a, 7b …… SrTiO3 thin film, 8a, 8b ... Source electrode, 9a, 9b ...
… Gate electrodes, 10a, 10b …… Drain electrodes, 11 …… La _1.5 Ba
_1.5 Cu ₃ Ox (6.5 <x <7.0) semiconductor thin film, 12 …… SrTiO ₃ (1
10) Single crystal substrate, 13 …… La _1.5 Ba _1.5 Cu ₃ Ox (6.5 <x <7.
0） Semiconductor thin film removed by etching, 14…
… La _1.5 Ba _1.5 Cu ₃ Ox (6.5 <x <7.0) A part where ions are implanted in a semiconductor thin film.

Front page continued (72) Inventor Tokumi Fukasawa 1-280, Higashi Koikeku, Kokubunji, Tokyo, Central Research Laboratory, Hitachi, Ltd. (72) Inventor Masahiko Hiratani 1-280, Higashi Koikeku, Kokubunji, Tokyo Hitachi Central Research Co., Ltd. In-house (72) Inventor Uki Kabazawa 1-280, Higashi-Kengokubo, Kokubunji-shi, Tokyo Inside Central Research Laboratory, Hitachi, Ltd. (56) Reference JP-A-3-148882 (JP, A)

Claims (3)

[Claims] 1. A substrate, a semiconductor layer made of an oxide formed on the substrate, and a plurality of superconducting elements made of a source, a drain, and a gate electrode on the semiconductor layer, the plurality of the semiconductor layers in the semiconductor layer. 2. A superconducting element, comprising means for preventing an interaction between the superconducting elements or between superconducting wirings due to the superconducting proximity effect in the semiconductor layer. 2. The superconducting element according to claim 1, wherein the means for preventing the interaction is an ion-implanted region formed in the semiconductor layer. 3. The superconducting element according to claim 1, wherein the means for preventing the interaction is a region where a part of the semiconductor layer is removed.