JPH08279630A - Manufacture of josephson-junction device - Google Patents

Abstract

PURPOSE: To obtain a method of manufacturing a Josephson-junction device which is large in a superconduction energy gap and easily manufactured. CONSTITUTION: A Josephson device composed of oxide superconductive layers and an oxide normal conductive layer sandwiched in between them is manufactured through such a manner that the surface of an oxide layer 11 is irradiated with argon ions to form an insulating layer 12 on it, and another oxide layer 13 is laminated.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a superconducting element, and more particularly to a method for manufacturing a Josephson junction element using an oxide superconductor.

[0002]

2. Description of the Related Art Most of electronic devices using high-temperature oxide superconductors are manufactured by using Josephson junctions. In recent years, Josephson junctions realized by using oxide high-temperature superconducting thin films are joined using artificial grain boundaries.
Step edge type joining, ramp edge type joining, laminated type joining and the like can be mentioned. When using a Josephson junction in a superconducting device including a superconducting transistor, a junction having a large superconducting energy gap is desired. this is,
This is because a junction having a large superconducting energy gap is expected to have improved characteristics in application. Since oxide high-temperature superconductors have a larger superconducting energy gap than metal-based low-temperature superconductors, the development of Josephson junction devices using oxide high-temperature superconductors is expected. However, any of the junctions that can be produced at present is a junction having the characteristics of superconductor-normal conductor-superconductor (S-N-S). In this junction, only a small superconducting energy gap can be theoretically obtained. In fact, the reported superconducting energy gap is not so large.

It is known that the superconducting energy gap is proportional to the product of the junction critical current (Ic) and the junction resistance (Rn). Generally, superconductivity-insulator-superconductivity (S-I-
The junction having the structure of S) has a high IcRn product,
That is, there is a high expectation for development because it has a large superconducting energy gap. In the above-mentioned joining using the artificial grain boundary or the step edge type joining, since the grain boundary (which becomes the normal conducting layer) is used in the barrier layer, it is essentially S-I-S.
Cannot make a joint. On the other hand, in the ramp edge type junction and the laminated type junction, the barrier material can be arbitrarily selected, and there is a possibility of realizing the S-I-S junction, but in reality, the barrier material is more barrier than the S-N-S junction. It is necessary to reduce the film thickness of the layer to a thickness of several Å, and there are no reports of S-I-S junctions up to now.

[0004]

When a material having a normal conductor characteristic is used for the barrier layer, the IcRn product of the junction becomes low as described above. This is because the order parameter is significantly reduced inside the superconductor at the interface between the barrier layer with low electrical resistance and the superconductor (J. Yoshida et a
l, Jpn.J.Appl.Phys., 31 1771 (1992)).

FIG. 4 shows the order parameter (Δ) of a superconductor, (a) is an S-N-S junction, and (b) is an S-.
It is a diagram which shows the simulation result in I-N-S junction. In the figure (a), S (YBCO (YbBa
Δ of S (YBCO) sharply decreases at the interface between ₂ Cu ₃ O _7-X oxide superconductor) and N (noble metal). In this figure, Φ ₀ is the wave function. On the other hand, figure (b)
In, since the insulator I is formed between S (YBCO) and N (noble metal), it can be seen that there is almost no change in Δ inside S (YBCO) and the wave function Φ ₀ hardly changes.

At the interface between the superconductor and the normal conductor, the quasi-particles in the normal conductor flow into the superconducting layer to reduce the order parameter (Δ) of the superconductor, while the SI
In the -NS junction, the insulating layer blocks the inflow of quasi-particles from the normal conductive layer, so it is considered that the order parameter in the superconductor does not decrease so much. Since the order parameter and the IcRn product are in a proportional relationship, the fact that the order parameter does not change means that the IcRn of the junction is large.

The present invention has been made in view of the above points, and an object thereof is to provide a Josephson junction element which is easy to manufacture and has a large superconducting energy gap by forming an SI junction in the Josephson junction element. It is in.

[0008]

According to the first aspect of the present invention, the above object is achieved by sequentially laminating a first oxide superconducting layer, an oxide normal conducting layer and a second oxide superconducting layer on a substrate. In the method for manufacturing a Josephson junction element, after laminating the first oxide superconducting layer, the surface of the first oxide superconducting layer is irradiated with argon ions on the surface of the first oxide superconducting layer. This is achieved by forming an insulating layer and then stacking the oxide normal-conducting layer and the second oxide superconducting layer.

According to a second aspect of the present invention, in a method for manufacturing a Josephson junction device, which comprises sequentially stacking a first oxide superconducting layer, an oxide normal conducting layer and a second oxide superconducting layer on a substrate, After laminating the first oxide superconducting layer and the oxide normal conducting layer, the surface of the oxide normal conducting layer is irradiated with argon ions to make the surface of the oxide normal conducting layer an insulating layer, and then the above This is achieved by stacking a second oxide superconducting layer.

According to a third aspect of the present invention, in a method for manufacturing a Josephson junction device, which comprises sequentially laminating a first oxide superconducting layer, an oxide normal conducting layer and a second oxide superconducting layer on a substrate, After laminating the first oxide superconducting layer, the surface of the first oxide superconducting layer is irradiated with argon ions to make the surface of the first oxide superconducting layer an insulating layer, and then the oxide normal conducting layer is formed. After laminating the layers, it is achieved by irradiating the surface of the oxide normal-conducting layer with argon ions to make the surface of the oxide normal-conducting layer an insulating layer, and then laminating a second oxide superconducting layer. .

[0011]

[Function] YBCO oxide superconductor and PBCO (PrBa)
_{When the 2} Cu ₃ O _7-y ) oxide normal conductor is irradiated with Ar ions, oxygen is released and an insulating layer is formed on the surface. The insulating layer is subjected to oxygen treatment in the later step of laminating the oxide superconducting layer and the oxide normal conducting layer. At this time, the insulating layer tries to recover to the superconducting layer or the normal conducting layer. However, under the film forming conditions of the oxide superconducting layer and the oxide normal conducting layer, the recovery is small and the insulating layer is left as it is.

According to the first invention, a SINS Josephson junction device is obtained. According to the second invention, SNIS
A Josephson junction device is obtained. According to the third invention, a SINIS Josephson junction element can be obtained.

[0013]

【Example】

Example 1 FIG. 1 shows a lamp-edge type Josephson junction element according to an example of the present invention, FIG. 1A is an SINS Josephson junction element, and FIG. It is sectional drawing of a NIS Josephson junction element.

FIG. 2 is a sectional view showing a manufacturing process of a lamp edge type Josephson junction element according to an embodiment of the present invention. In this embodiment, first, a YBCO layer 1 is formed on a SrTiO ₃ (100) (hereinafter referred to as STO) single crystal substrate 10.
1 is deposited to a thickness of 100 nm, and the STO layer 15 is formed thereon.
Was deposited to a thickness of 300 nm (FIG. 2 (a)). At this time, the STO layer 15 serves as an interlayer insulating layer that prevents a short circuit between the upper and lower YBCO layers. The two layers were deposited using an rf sputtering device at a substrate temperature of 700 ° C. and a sputtering pressure of 0.5 Pa (Ar / O 2 = 1). The produced thin films are all c-axis oriented. Then, this two-layer film is
The substrate was diagonally cut by V Ar ion milling (Fig. 2).
(B)). At this time, the surface of the YBCO layer 11 that was diagonally cut was about 10 ³ Ω · cm in the measurement of the film prepared under the same conditions.
It is known that the insulating layer 12 having the resistivity of is formed. Next, PrBa ₂ Cu ₃ is formed on the insulating layer 12.
O _7-y layer 13 (PBCO layer 13) with a thickness of 30 nm, YB
The CO layer 14 was continuously deposited to a thickness of 100 nm in the same chamber (FIG. 2 (c)). PBCO layer 13, YBCO
While the layer 14 is being formed, oxygen annealing is substantially performed.
This condition (700 ° C, Ar / O2 = 1, 0.5 Pa, 2
It has been confirmed that the insulating layer does not recover at 0 minutes). Finally, microfabrication using ordinary photolithography was performed so as to have a bridge with a width of 1 μm, and the device was completed (FIG. 2D). The above process is a step of forming an S-I-N-S junction. However, when forming an S-I-N-I-S junction, Ar plasma is sputtered after depositing the PBCO layer 13. The surface of the PBCO layer 13 may be generated in the device to form an insulating layer, and then the YBCO layer 14 may be deposited to form the layer.

The junction element thus manufactured operated as a Josephson junction element. Table 1 shows the measured temperature of 4.
S-N-S, S-I-N-S, S-I-N-I at 2K
The value of IcRn product when the N layer thickness of the -S Josephson junction element is 30 nm is shown.

[0016]

[Table 1] The S-N-S Josephson junction element has a PBCO layer and a YBC.
Oxygen was introduced into the chamber before the deposition of the O layer, and annealing was carried out for 1 hour to erase the insulating layer, thereby forming the original superconducting layer or normal conducting layer.

S-N-S Josephson Junction Element, S-I
It can be seen that the IcRn product increases in the order of the -N-S Josephson junction device and the S-I-N-I-S Josephson junction device. The IcRn product is represented by the following formula. Where Δ ₁ and Δ ₂ are the order parameter magnitudes at the two superconducting interfaces. From this formula, S-I-N-
It can be seen that the I-R Josephson junction device has a larger IcRn product than the S-I-N-S Josephson junction device. Embodiment 2 FIG. 3 shows a stacked type Josephson junction element according to another embodiment of the present invention, FIG.
3A is a cross-sectional view showing an enlarged S-I-N-S Josephson junction element of FIG. 1A, and FIG. 3C is an enlarged S-I-N-I-S Joseph part of FIG. It is sectional drawing which shows a Son junction element. The substrate was STO (100) as in Example 1.
The substrate 20 is used, and the lower electrode YBCO 21,
The upper electrode YBCO23 and the barrier layer PBCO22 were selected. In the case of the laminated type, the film formation temperature was set to 650 ° C., and the a-axis alignment film was used for all. In the case of the laminated type, the insulating layer 24A was formed by depositing the lower electrode YBCO 21 and then raising Ar plasma in the chamber. After that, a barrier layer PBCO22 and an upper electrode YBCO23 were continuously formed to fabricate an SINS Josephson junction element. Alternatively, after depositing the barrier layer PBCO22 again,
An insulating layer 24B was formed by standing Ar plasma, and an upper electrode YBCO 23 was deposited to manufacture an S-I-N-I-S Josephson junction device. As a result of measuring the obtained device, the same result as in Example 1 was obtained.

[0018]

According to the present invention, the surface of one of the oxide superconducting layer and the oxide normal conducting layer is irradiated with argon ions to form an insulating layer, and then the other oxide layer is laminated. Therefore, the insulating layer does not recover to the superconducting layer or the normal conducting layer when the other oxide layer is laminated, the insulating layer remains as it is, and the SINS junction or the SINS junction having a high IcRn product is obtained.
A Josephson junction element of NIS junction or SINIS junction can be easily obtained.

[Brief description of drawings]

1 shows a ramp-edge type Josephson junction device according to an embodiment of the present invention, FIG. 1 (a) is an SI-N-S Josephson junction device, and FIG. 1 (b) is an SI-N- Sectional view of the IS Josephson junction device

FIG. 2 is a sectional view showing a manufacturing process of a ramp-edge type Josephson junction element according to an embodiment of the present invention.

3A and 3B show stacked Josephson junction devices according to different embodiments of the present invention. FIG. 3A is an overall cross-sectional view, and FIG. 3B is an enlarged S-I-N part of FIG. -S Josephson junction element cross-sectional view, FIG. 6C is a cross-sectional view showing the SI-NI-IS Josephson junction element in which the main part of FIG.

4A and 4B show order parameters (Δ) of a superconductor, FIG. 4A is an S-N-S junction, and FIG.
-Schematic of simulation results for S-junction

[Explanation of symbols]

 10 STO (100) Substrate 11 YBCO Layer 12 Insulating Layer 12A Insulating Layer 13 PBCO Layer 14 YBCO Layer 15 STO Layer 20 STO (100) Substrate 21 Lower Electrode YBCO 22 Barrier Layer PBCO 23 Upper Electrode YBCO 24A Insulating Layer 24B Insulating Layer

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Taehide Yamaguchi 1-1 Tanabe Nitta, Kawasaki-ku, Kawasaki-shi, Kanagawa Fuji Electric Co., Ltd. (72) Inventor Hiroshi Kamijo 1 Nitta, Tanabe-ku, Kawasaki-ku, Kanagawa Prefecture No. 1 within Fuji Electric Co., Ltd.

Claims (3)

[Claims] 1. A method of manufacturing a Josephson junction device comprising a first oxide superconducting layer, an oxide normal conducting layer and a second oxide superconducting layer which are sequentially laminated on a substrate, wherein the first oxidation is performed. First superconducting layer, the surface of the first oxide superconducting layer is irradiated with argon ions to form an insulating layer on the surface of the first oxide superconducting layer, and then the normal oxide conducting layer and the second superconducting layer are formed. A method for manufacturing a Josephson junction device, comprising: stacking the oxide superconducting layer of 1. 2. A method for manufacturing a Josephson junction device, which comprises sequentially stacking a first oxide superconducting layer, an oxide normal conducting layer, and a second oxide superconducting layer on a substrate. Object superconducting layer and the oxide normal conducting layer are laminated, the surface of the oxide normal conducting layer is irradiated with argon ions to make the surface of the oxide normal conducting layer an insulating layer, and then the second oxide. A method for manufacturing a Josephson junction device, which comprises laminating superconducting layers. 3. A method for manufacturing a Josephson junction device, which comprises sequentially stacking a first oxide superconducting layer, an oxide normal conducting layer and a second oxide superconducting layer on a substrate. Object superconducting layer is laminated, the surface of the first oxide superconducting layer is irradiated with argon ions to make the surface of the first oxide superconducting layer an insulating layer, and then the oxide normal conducting layer is laminated. The production of a Josephson junction device characterized in that the surface of the oxide normal conducting layer is irradiated with argon ions to make the surface of the oxide normal conducting layer an insulating layer, and then a second oxide superconducting layer is laminated. Method.