JPH05327047A - Josephson element and manufacture thereof - Google Patents

Abstract

PURPOSE:To obtain a Josephson element which can be highly integrated by obtaining a film of high quality even if a crystal growing direction of a superconducting material and a direction of excellent coherence are difference and realizing a planar structure by providing an intermediate layer as a sidewall. CONSTITUTION:A first superconductor layer 2 is formed on a first surface region of a substrate 1. An intermediate layer 3 is formed on a second substrate surface region adjacent to a first substrate surface region, in contact with the layer 2, and brought into contact with a second superconductor layer 4 at a side parallel to its contact surface through a thickness of the layer 3. A second superconductor layer 4 is formed on a third substrate surface region opposed to the first substrate surface region, and a first electrode 5, a second electrode 6 are connected to the layers 2, 4. Thus, a Josephson junction is realized in a horizontal direction with excellent coherence, and a planar structure in which the layers 2, 3, 4 are sequentially aligned in a horizontal direction is realized on the surface of the substrate 1.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a Josephson device which is a high speed digital logic device and a method of manufacturing the Josephson device.

[0002]

2. Description of the Related Art Si and GaAs are used as digital logic elements.
An integrated circuit using a semiconductor such as is widely used and used. In response to the increasing demand for high-speed computation, Josephson devices that operate on a completely different principle from these semiconductor devices and have a dramatically short switching time have been proposed and prototyped. The integration of Josephson devices, which started using Pb alloy-based materials, has evolved while changing the materials to Nb-based compound materials that exhibit more stable superconducting properties. In recent years, with the discovery of Bi-based and Y-based oxides that are in a superconducting state at a higher temperature than known superconducting materials, Josephson devices using these superconducting materials with Nb-based compounds, and fusion with semiconductor technology Attention has been paid to integrated circuits.

Conventionally, a superconductor layer (hereinafter referred to as a first superconductor layer) / a non-superconductor layer (hereinafter referred to as an intermediate layer) /
In manufacturing a Josephson device having a sandwich type structure of a superconductor layer (hereinafter, referred to as a second superconductor layer),
There is known a method of using a multilayer film in which a superconductor thin film, a non-superconductor thin film, and a superconductor thin film are stacked in this order in the vertical direction of a substrate. For example, as an Nb system, H. Nakagawa et a
l., 1990 Applied Superconductivity Conf., EPR-1.01
, Y system, CTRogers et al., Appl.Phys.Lett.5
5,2032 (1989), and as the Bi system, K. Mizuno et al.,
Appl. Phys. Lett. 56, 1469 (1990), etc. have been reported, but all have a laminated multilayer film structure.

FIG. 3 is a block diagram of such a Josephson device. As shown in the figure, the first superconductor layer 2, the intermediate layer 3, and the second superconductor layer 4 are sequentially stacked in parallel with the surface of the substrate 1,
It realizes Josephson junction. The first electrode 5 and the second electrode 6 are connected to the first superconductor layer 2 and the second superconductor layer 4, respectively, and are used for voltage application and current supply between the two superconductor layers.

Since this Josephson element is constructed as described above, when forming a multilayer film before etching, it is unavoidable to provide a junction surface in the crystal growth direction of the material of each layer, and heteroepitaxy (existence). Growing a crystal of a different substance on the crystal material of the substance) to form an intermediate layer 3 made of a non-superconductor material on the first superconductor layer 2.
It is necessary to perform it when forming the second superconductor layer 4 on the intermediate layer 3.

[0006]

As the crystal of the superconductor material used, the direction in which the coherence property is good and the growth direction in which the good quality film is obtained may be different. In such a case, in the conventional manufacturing method, since the crystal growth direction and the junction direction of the superconducting material coincide with each other as described above, it is difficult to obtain a good quality Josephson element.

When the Josephson junction is implemented by heteroepitaxy, it is necessary that the lattice mismatch between the crystals of the two materials is small, the adhesion and the coverage are good. Therefore, in the superconductor layer material and the intermediate layer material, Its crystal structure had to be similar. For example, as the material of the superconducting layer, selecting the Bi based or Y-based oxide, from its crystal structure is a perovskite structure and the requirements, in the Y-based as the intermediate layer material PrBa ₂ Cu ₃
In the case of Bi system such as O _y , one having a perovskite structure with a relatively small lattice constant mismatch such as Bi ₂ Sr ₂ CuO _x had to be selected.

Further, the conventional Josephson element has a planar structure because the first superconductor layer 2, the intermediate layer 3, and the second superconductor layer 4 are sequentially stacked in the direction perpendicular to the substrate as described above. It was difficult to achieve high integration.

According to the present invention, a Josephson element and a Josephson element configured so that a high quality element can be obtained even in the crystal structure of a superconducting material when the direction of good coherence does not coincide with the direction of crystal growth capable of obtaining a high quality film. Along with providing a manufacturing method thereof, based on the crystal structure of the superconducting material as described above, a constraint condition such as a perovskite intermediate layer material is removed in the perovskite structure superconducting material,
The purpose is to broaden the selection range of intermediate layer materials.

It is another object of the present invention to provide a Josephson device and a manufacturing method which can be highly integrated by realizing a planar structure.

[0011]

In the Josephson element of the present invention, the intermediate layer is provided as a side wall obtained by the side wall forming method which is carried out in the semiconductor element, so that the crystal growth direction of the superconducting material is crossed. The feature is that the superconductor layer and the intermediate layer made of a non-superconducting material can be joined together and a planar structure is realized.

The method of manufacturing the Josephson element of the present invention further comprises a first step of forming a first superconductor layer on the substrate and an electrode connected to this layer on the first superconductor layer, A second step of forming an intermediate layer by using a reactive ion etching method as a side wall of the first superconductor layer, and a second superconducting layer on the opposite side of the first superconductor layer with the intermediate layer interposed therebetween. Third step of forming a body layer using a selective crystal growth method and fourth step of forming an electrode connected to the second superconductor layer
And the steps of.

[0013]

According to the Josephson device of the present invention, the Josephson junction direction and the crystal growth direction at the time of forming the superconducting layer thin film can be made to intersect with each other. Even if the good direction is different, the superconductor layer obtained by growing the good quality film in the crystal direction can be bonded in the direction with good coherence and realizes a planar structure, thus achieving high integration. Can be converted.

According to the method for manufacturing the Josephson device of the present invention, since the intermediate layer is provided by forming the side wall, the heteroexamination for forming the intermediate layer on the superconducting layer and the superconducting layer on the intermediate layer, which have been conventionally required, can be obtained. No longer need it. Therefore, it is possible to remove the constraint that the crystal structure must have a crystal structure similar to that of the superconductor material in selecting the intermediate layer material.

Further, according to the method for manufacturing the Josephson device of the present invention, the first superconductor layer, the intermediate layer and the second superconductor layer are sequentially formed on the substrate in the horizontal direction with respect to the substrate surface. It is possible to manufacture the above Josephson device having a planar structure and operating well.

[0016]

Embodiments of the present invention will be described with reference to the drawings.
FIG. 1 shows the structure of the Josephson device of the first embodiment. In this Josephson element, the substrate 1 is NdGaO ₃ (110), the first superconducting layer 2 and the second superconducting layer 4 are YBa ₂ Cu ₃ O _7-x , and the intermediate layer 3 is SiO 2. ₂ and Al is used for the first electrode 5 and the second electrode 6. YBa ₂ Cu ₃ O _7-x , which is the material of the first superconductor layer 2 and the second superconductor layer 4, has a crystal structure based on a perovskite structure and has good coherence in the a-axis direction. There is a property that a high quality film can be easily obtained by crystal growth in the c-axis direction orthogonal to the axis.

The geometrical arrangement of the constituent elements of this Josephson element is as follows. The first superconductor layer 2 is
The crystal structure is formed on the first substrate surface region and has a c-axis direction in the vertical direction of the substrate 1 surface, an a-axis direction in the horizontal direction, and a side surface orthogonal to the a-axis direction. The intermediate layer 3 is formed on the second substrate surface region adjacent to the first substrate surface region, contacts one side surface of the first superconductor layer 2 orthogonal to the a-axis direction, and reduces the thickness of the intermediate layer 3 The side surface parallel to the contact surface is in contact with the second superconductor layer 4. Second
The superconductor layer 4 is in contact with the second substrate surface region,
It is formed on the third substrate surface region opposite to the first substrate surface region with this region as a boundary, and its crystal structure is:
The c-axis direction is vertical to the surface of the substrate 1 and the a-axis direction parallel to the a-axis direction of the first superconductor layer 2 is horizontal. The first electrode 5 and the second electrode 6 are respectively the first superconductor layer 2 and the second superconductor layer 2.
It is connected to the superconductor layer 4.

Since the Josephson element is constructed with the above structure, as the material crystals of the first superconductor layer 2 and the second superconductor layer 4, the surface of the substrate 1 on which crystal growth is carried out in the c-axis direction in which a good quality film can be obtained. And the Josephson junction is realized in the a-axis direction with good coherence. Also, a planar structure is realized as a structure in which the first superconductor layer 2, the intermediate layer 3, and the second superconductor layer 4 are arranged in this order on the surface of the substrate 1 in the horizontal direction.

This Josephson device is manufactured by the process shown in FIG.

First, the first superconductor layer 2 is formed on the substrate 1 by the crystal growth in the c-axis direction of the perovskite structure, which is the crystal structure of the material, by the sputtering method. After that, the first electrode 5 connected to the first superconductor layer 2 is formed (FIG. 2A).

Next, after masking the portion to be left as the first superconductor layer 2, etching is performed to partially expose the surface of the substrate 1 (FIG. 2B). Next, the intermediate layer 3 is formed on the entire exposed surface in the process step of FIG. 2B by the low pressure CVD method (FIG. 2C). After this, reactive ion etching (R
Directional etching by IE) is performed to provide the intermediate layer 3 with a width of 5 nm on the side wall of the first superconductor layer 2 (FIG. 2).
(D)). In the RIE at this time, CF ₄ is used as the reaction gas.
To use.

Subsequently, the second superconductor layer 4 is formed on the surface of the substrate 1 exposed in the process step of FIG. 2D by selective crystal growth (FIG. 2E). After this, the second electrode 6 connected to the second superconductor layer 4 is formed.

In the above steps, a Josephson device was produced without using hetero-excitation, and a Shapiro step was observed by microwave irradiation of 12 GHz, and it was confirmed that a good Josephson device could be obtained.

Next, the second embodiment will be described. The configuration diagram of the Josephson element of the second embodiment is the same as that of the first embodiment, and only the materials used are different. In this Josephson element, as a material, MgO (100) was used for the substrate 1.
On the first superconducting layer 2 and the second superconducting layer 4 with Bi ₂
Sr ₂ Ca ₂ Cu ₃ O _x was _added to the intermediate layer 3 as Bi ₂ Sr ₂ C.
uO _x is applied to the first electrode 5 and the second electrode 6 by Ag or A
u are used. As in the first embodiment, the material of the first superconductor layer 2 and the second superconductor layer 4 is Bi ₂ Sr ₂
The crystal structure of Ca ₂ Cu ₃ O _x is basically a perovskite structure and has good coherence in the a-axis direction, while it is easy to obtain a high-quality film by crystal growth in the c-axis direction orthogonal to the a-axis direction. There is a property.

Since the Josephson device is formed by using the above materials in the same manner as in the first embodiment, the first superconductor layer 2,
As the material crystal of the second superconductor layer 4, the c-axis direction in which a good quality film is obtained is set to the direction perpendicular to the surface of the substrate 1 for crystal growth, and the Josephson junction is realized in the a-axis direction with good coherence. ing. In addition, on the surface of the substrate 1, the first superconductor layer 2, the intermediate layer 3,
A planar structure is realized as a structure in which the superconductor layers 4 are arranged in order.

The manufacturing process of this Josephson device is shown in FIG.
The manufacturing process is the same as that of the first embodiment shown in FIG. 3, the composition of the reaction gas of RIE used for forming the intermediate layer 3 is BCl ₃ + Cl ₂ , and the forming width of the intermediate layer 3 is 6
The difference is 0 nm.

In the above steps, a Josephson device was prepared without using hetero-excitation, and a Shapiro step was observed by microwave irradiation of 18 GHz, and it was confirmed that a good Josephson device could be obtained.

The present invention is not limited to the above embodiment, but various modifications can be made.

For example, as the intermediate layer material of the first embodiment, in addition to SiO ₂ , SiN, SiO _x N _y , MgO, N
dGeO _3, or the like may be used. Further, in forming the intermediate layer of the first embodiment, not only the low pressure CVD method but also the atmospheric pressure CVD method, the plasma CVD method, the sputtering method, the ECR-CVD method or the like may be used depending on the intermediate layer material.

[0030]

As described above in detail, according to the present invention, even when the crystal growth direction in which a high quality film is obtained as the superconductor layer and the direction in which the coherence is good as the crystal are different, the high quality film is obtained. It is possible to manufacture a planar type Josephson element which can be highly integrated in a process which has a junction in a direction of good coherence while expecting stable operation, can expect stable operation, and has a small yield in manufacturing.

[Brief description of drawings]

FIG. 1 is a configuration diagram of a Josephson device according to a first embodiment.

2A to 2C are manufacturing process diagrams of the Josephson device of FIG.

FIG. 3 is a block diagram of a conventional Josephson device.

[Explanation of symbols]

1 ... Substrate, 2 ... First superconductor layer, 3 ... Intermediate layer, 4 ... Second
Superconductor layer, 5 ... First electrode, 6 ... Second electrode.

Claims (2)

[Claims] 1. A first layer of a superconducting material formed on a first region of a substrate surface, and a non-superconducting material formed on a second region of the substrate surface adjacent to the first region. And a third layer made of a superconducting material formed in a third region of the substrate surface which is adjacent to the second region and faces the first region with the second region as a boundary. A planar Josephson device comprising: a layer; and a structure in which the first layer and the second layer are joined and the second layer and the third layer are joined. 2. A first step of growing a superconductor layer on the entire surface of the substrate, and a second step of removing the superconductor layer other than the first region of the surface of the substrate to form a first layer. A third step of depositing a non-superconducting material on the entire exposed surface to form a non-superconducting layer, and removing the non-superconducting layer other than the side surface of the first layer using a reactive ion etching method. A fourth step of forming a second layer on a second region of the substrate surface as a sidewall of the first layer, and a third region opposite to the first region with the substrate surface as a boundary. A fifth step of selectively growing a crystal of a superconducting material to form a third layer, the method of manufacturing a Josephson device.