JPH06120577A - Manufacturing method of artificial grain boundary - Google Patents

Abstract

(57) [Abstract] [Purpose] By selectively growing thin films with different in-plane crystallographic orientations and forming artificial crystal grain boundaries at arbitrary positions on the substrate,
For example, Josephson junctions and crystal grain boundaries exhibiting the PTC effect are easily manufactured with high integration. [Structure] A buffer layer 2 made of magnesium oxide is formed on a part of a strontium titanate (001) substrate 1, and a bismuth-based oxide superconducting film is formed on both the substrate 1 and the buffer layer 2. Oxide superconducting film 3 formed on the substrate 1 and oxide superconducting film 4 formed on the buffer layer 2.
The crystal grain boundaries 5 were artificially formed by changing the in-plane orientation of a.

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 an artificial grain boundary, and more particularly to a Josephson junction using an oxide superconducting film and a PTC (Positive) which are necessary for manufacturing a superconducting element.
The present invention relates to a method for manufacturing an artificial grain boundary exhibiting a PTC effect using a ferroelectric film necessary for manufacturing a thermistor.

[0002]

2. Description of the Related Art Since the oxide superconductor film surface is easily transformed in the atmosphere and the coherence length is short, it is difficult to form a tunnel-type Josephson junction used in conventional metal-based superconductors. is there. Therefore, it is advantageous to form a grain boundary junction type Josephson junction utilizing the crystal grain boundaries peculiar to an oxide superconductor in order to manufacture a quantum interference device that can be applied to a magnetic sensor. A method of artificially forming a grain boundary junction type Josephson junction has been implemented. FIG. 7 shows, for example, Applied Physics Letter Vol.57,
It is explanatory drawing which shows the manufacturing method of the grain boundary junction type Josephson junction shown by L727 (1990). In the figure, 8 is a bicrystal strontium titanate (100) substrate, 9 is a yttrium-based oxide superconducting film, and 10 is a grain boundary junction.

The conventional artificial grain boundary junction type Josephson junction is formed as described above. That is, two strontium titanate single crystal planes 8a and 8b which are deviated from each other are sintered and bonded to each other to produce a bicrystal substrate 8 having a grain boundary, and an oxide superconducting film 9 is grown thereon. ,
The crystal grain boundary junction portion 10 corresponding to the grain boundary of the substrate 8 is formed in the oxide superconducting film.

Further, in the ceramic, as shown in the schematic view of FIG. 8, many kinds of interfaces called grain boundaries exist. Ferroelectric ceramics such as barium titanate can be made into a semiconductor by adding impurities, but at this time, since a Schottky barrier is generated at the grain boundary, as shown in the characteristic diagram of FIG. It exhibits a phenomenon in which the electric resistance rapidly increases with the temperature near the Curie temperature, that is, a so-called PTC effect. The temperature sensor applying this effect is P
It has already spread as a TC thermistor.

[0005]

The conventional method of manufacturing the Josephson junction as described above requires complicated and precise steps such as sintering and joining the strontium titanate substrates, and the joining portion is Since it is limited to the junction part of the substrate, there is a problem that the degree of integration cannot be increased because the degree of freedom in circuit design is lost when the Josephson junction is integrated.

Further, since the above-described conventional crystal grain boundaries exhibiting the PTC effect are a plurality of grain boundaries naturally formed in the ceramic, various characteristics obtained therefrom are average values at the plurality of grain boundaries. However, there is a problem that there is a limit to the sensitivity in the vicinity of the transition point in the resistance temperature characteristic shown in FIG.

The present invention has been made in order to solve such a problem, and artificial grain boundaries are formed at arbitrary positions on a substrate to form, for example, Josephson junctions or grain boundaries exhibiting the PTC effect. It is an object of the present invention to provide a method for manufacturing an artificial grain boundary, which can be simply manufactured with a high degree of integration.

[0008]

According to the method for producing an artificial grain boundary of the present invention, a buffer layer made of a substance different from the substrate is formed on a part of the substrate, and the buffer layer is formed on both the substrate and the buffer layer. A thin film is formed, and a crystal grain boundary is artificially formed by changing the in-plane orientations of the thin film formed on the substrate and the thin film formed on the buffer layer.

Further, an oxide superconducting film is formed as a thin film.

Further, the film forming conditions of the oxide superconducting film are adjusted to control the mismatch angle of the grain boundary junction.

Then, a ferroelectric film is formed as a thin film.

[0012]

In the method of manufacturing an artificial grain boundary of the present invention, a buffer layer is formed on a part of the substrate by using, for example, a photolithography technique, so that, for example, (001) orientation between the substrate and the buffer layer is formed. Since the in-plane crystal orientation of the thin film can be changed, thin films having different in-plane crystal orientations can be selectively grown on this substrate at arbitrary places. Since the differently oriented portions in the thin film form grain boundaries, the grain boundary junction of the thin film can be formed at any place on the substrate.

Further, by forming the oxide superconducting film as a thin film, it is possible to form a crystal grain boundary junction portion of the oxide superconducting film at an arbitrary position on the substrate, and by using this, a Josephson junction can be simply formed. It can be manufactured with high integration.

Furthermore, the misalignment angle of the grain boundary junction can be controlled by adjusting the film forming conditions of the oxide superconducting film, and the rotation angle of the grain boundary junction can be formed at a desired angle. It is possible to increase the critical current by making it smaller than 45 degrees.

By forming the ferroelectric film as a thin film, the grain boundary junction of the ferroelectric film can be formed independently at any place on the substrate, and the PTC effect can be obtained by using this. Can be produced.

[0016]

EXAMPLES Example 1. FIG. 1 is an explanatory view showing an embodiment of a method for manufacturing an artificial grain boundary according to the present invention and an example of a method for manufacturing a Josephson junction. 1 is strontium titanate (00
1) a substrate, 2 a buffer layer made of magnesium oxide,
3 is a (001) -oriented bismuth-based oxide superconducting film whose a-axis or b-axis is made of strontium titanate and is parallel to the [110] direction. The (001) -oriented bismuth-based oxide superconducting film 5 parallel to the [100] direction is a grain boundary junction. FIGS. 2A and 2B are waveform charts showing X-ray diffraction patterns for explaining control of in-plane crystal orientation of the oxide superconducting film. (A) is an X-ray diffraction pattern of (02 20 ) reflection of a bismuth-based oxide superconducting film 3 grown on a strontium titanate (001) substrate 1,
(B) is the (02 20 ) reflection X of the bismuth oxide superconducting film 4 grown on the buffer layer 2 of magnesium oxide formed on the strontium titanate (001) substrate 1.
It is a line diffraction pattern. As shown in FIG. 2, a bismuth superconducting film 3 grown on a strontium titanate (001) substrate 1 and a bismuth superconducting film 4 grown on a buffer layer 2 made of magnesium oxide formed on the substrate 1. In and, the in-plane crystal orientation is rotated by 45 degrees.

Next, a method of manufacturing the Josephson junction according to this embodiment will be described. First, as shown in FIG. 1, a buffer layer 2 made of magnesium oxide is formed on a part of a strontium titanate (001) substrate 1 by using a photolithography technique.
To a thickness of 50 to 150 Å, in this case 100 Å, and bismuth oxide superconducting films 3 and 4a are formed on the substrate 1 and the buffer layer 2 over both of them in this case by a thickness 1500 Å sputtering method. . Target composition Bi: S
r: Ca: Cu: O = 2: 2.1: 2.3: 3.45:
X, the substrate temperature was 650 ° C. The bismuth-based oxide superconducting film 3 on the substrate 1 grows in the (001) orientation on the substrate 1, but within the plane of the substrate 1, the bismuth-based oxide superconducting film 3 is formed.
Has its a-axis or b-axis oriented parallel to the [110] of the substrate 1. On the other hand, the bismuth-based oxide superconducting film 4 on the buffer layer 2 grows on the buffer layer 2 with (001) orientation. The axis is oriented parallel to [100] of the substrate 1.

Thus, if a bismuth oxide superconducting film is formed on the substrate 1 partially provided with the buffer layer 2 by, for example, a sputtering method, the oxide superconducting is artificially performed along the edge of the buffer layer 2. The crystal grain boundary junction portion 5 of the film can be formed at an arbitrary position, and a Josephson junction can be easily manufactured using this. Further, the buffer layer 2 can be finely formed in a desired pattern with high density, the degree of integration is enhanced, and the compatibility with the micro process is improved.

Example 2. FIG. 3 is an explanatory view showing a Josephson junction obtained by another embodiment of the method for manufacturing the Josephson junction of the present invention. 1 is a strontium titanate (001) substrate, 2 is a buffer layer made of magnesium oxide, 3 is a (001) -oriented bismuth-based oxide whose a-axis or b-axis is parallel to the [110] direction of the substrate made of strontium titanate Superconducting film, 4b has a-axis or b-axis made of strontium titanate

[0020]

[Outer 1]

The oxide superconducting films 5 are grain boundary junctions. FIG. 4 shows X indicating the in-plane crystal orientation of the oxide superconducting film 4b.
It is a waveform diagram of a line diffraction pattern. That is, it is the (02 16 ) reflection X-ray diffraction pattern of the bismuth-based oxide superconducting film 4b grown on the magnesium oxide buffer layer 2 formed on the strontium titanate (001) substrate 1.

Next, a method of manufacturing the Josephson junction of this embodiment will be described. First, the buffer layer 2 made of magnesium oxide is formed on a part of the strontium titanate (001) substrate 1 using the photolithography technique as in the above-described embodiment. Then, bismuth-based oxide superconducting films 3 and 4b are formed on the substrate 1 and the buffer layer 2 by a sputtering method so as to extend over both of them. In this case, the target composition Bi: Sr: Ca: Cu: O = 2: 2.1: 1.1
It was carried out under the film forming conditions of 5: 2.3: X and a substrate temperature of 660 ° C. Since magnesium oxide grows on the strontium titanate substrate (001) surface with the magnesium oxide [100] direction parallel to strontium titanate [110], a photolithography technique is applied to a part of the strontium titanate (001) substrate 1. When the buffer layer 2 made of magnesium oxide is used, the bismuth-based oxide superconducting film 3 on the substrate 1 grown under the above film forming conditions grows in the (001) orientation on the substrate 1, Then, in the bismuth-based oxide superconducting film 3, its a-axis or b-axis is the substrate 1
Oriented parallel to the [110] of. On the other hand, the bismuth oxide superconducting film 4b on the buffer layer 2 is
Although the bismuth-based oxide superconducting film 4b grows with the (001) orientation above, the a-axis or b-axis of the bismuth-based oxide superconducting film 4b is [51

[0023]

[Outside 2]

If a bismuth-based oxide superconducting film is formed on the digitized substrate 1 by, for example, a sputtering method under the above-mentioned film forming conditions, the bismuth-based oxide superconducting film 33.7 is artificially formed along the edge of the buffer layer 2. The rotated grain boundary junction 5 can be formed at an arbitrary location, and a Josephson junction can be easily manufactured using this. In the above example, the rotation angle of the grain boundary bonding was 45 degrees,
In this embodiment, the rotation angle is small, and the critical current of the junction can be increased accordingly.

Example 3. FIG. 5 is an explanatory view showing still another embodiment of the method for producing an artificial grain boundary of the present invention, an example of a method for producing an artificial grain boundary exhibiting a PTC effect, and a PTC thermistor. 13 is a barium titanate film which is a ferroelectric film of (001) orientation parallel to the [110] direction of the substrate whose a-axis or b-axis is strontium titanate, and 14 is a strontium titanate whose a-axis or b-axis is made. Substrate [10
A barium titanate film having a (001) orientation parallel to the [0] direction is a grain boundary junction.

As in Example 1, a magnesium oxide buffer layer 2 was formed on a part of a strontium titanate (001) substrate 1 by photolithography, and both were formed on the substrate 1 and the buffer layer 2. Barium titanate films 13 and 14 which are ferroelectric films are formed over the entire area. The barium titanate film 13 on the substrate 1 grows in the (001) orientation on the substrate 1, but in the plane of the substrate 1, the barium titanate film 1 is formed.
3 has its a-axis or b-axis oriented parallel to [110] of the substrate 1. On the other hand, the barium titanate film 14 on the buffer layer 2 grows in the (001) orientation on the buffer layer 2, but in the plane of the substrate 1, the barium titanate film 14 has its a-axis or b-axis aligned with the substrate 1. Oriented parallel to [100]. Therefore, if a barium titanate film is formed on the substrate 1 partially provided with the buffer layer 2 by, for example, the sputtering method, artificially along the edge of the buffer layer 2, the grain boundary junction of the ferroelectric film is formed. 5 can be formed independently at any place, and by using this, an artificial grain boundary exhibiting the PTC effect can be easily produced. FIG. 6 is a characteristic diagram showing resistance temperature characteristics in the single artificial grain boundary junction formed as described above. It can be seen that the slope at the transition temperature is steeper as compared with the conventional one using a plurality of crystal grain boundaries naturally formed in the ferroelectric ceramic. A highly sensitive PTC thermistor can be obtained. In addition, since this single grain boundary can be selectively formed, that is, the buffer layer 2 can be formed in a desired pattern minutely and with high density, the degree of freedom in circuit design can be increased and the degree of integration can be increased. be able to.

Example 4. Further, in Example 1 above, a strontium titanate (001) substrate was used as the substrate,
Although the case where magnesium oxide is used for the buffer layer and the bismuth-based oxide superconducting film is formed as the thin film is shown, a magnesium oxide (001) substrate may be used as the substrate and strontium titanate may be used for the buffer layer. A (001) -oriented bismuth-based oxide superconducting film having a-axis or b-axis made of magnesium oxide and parallel to the [100] direction of the substrate is formed on the substrate, and the a-axis or b-axis is formed on the strontium titanate buffer layer. A (001) -oriented bismuth-based oxide superconducting film whose axis is parallel to the [110] direction of the substrate made of magnesium oxide is formed, and the same effect as in Example 1 is obtained.

Example 5. Similarly, in the second embodiment, the case where a strontium titanate (001) substrate is used as a substrate, magnesium oxide is used as a buffer layer, and a barium titanate film of a ferroelectric film is formed as a thin film is shown. Alternatively, a magnesium oxide (001) substrate may be used as the substrate and strontium titanate may be used as the buffer layer, and the same effect as in Example 2 is obtained.

In the above embodiments, the strontium titanate (001) substrate and the magnesium oxide (001) substrate are used as the substrate, but other substrates may be used and the same effect can be obtained. Although the case where magnesium oxide or strontium titanate is used for the buffer layer is shown, other materials such as stabilized zirconia or selenium oxide may be used and the same effect can be obtained. further,
Although an example of a bismuth-based oxide superconducting film is shown as the oxide superconducting film, other oxide superconducting films such as a yttrium-based superconducting film may be used, and the same effect is obtained. Furthermore, although the example of the barium titanate film is shown as the ferroelectric film, another ferroelectric film may be used and the same effect can be obtained. As a method for forming the buffer layer and the oxide superconducting film, a general film forming method such as sputtering is used.

Further, although it is difficult to integrate the crystal grain boundaries exhibiting the PTC effect, which have not been artificially manufactured in the past, and complicated steps are required, it is difficult to integrate them. It can be artificially formed. That is, two single crystal planes having different orientations are bonded to each other to produce a bicrystal substrate having grain boundaries. For example, strontium titanate whose two in-plane crystal orientations are rotated by 45 degrees is used as two single crystal planes with different orientations, and they are sintered and joined so that they are symmetrical at the joint. By forming a ferroelectric film, for example, a barium titanate film, on this substrate, crystal grain boundaries exhibiting the PTC effect corresponding to the grain boundaries of the substrate are artificially produced. Similar to the case of the method for manufacturing an artificial grain boundary of the present invention, the slope of the resistance temperature characteristic at the transition point becomes steep, and a highly sensitive PTC thermistor can be realized.

[0031]

As described above, according to the present invention, a buffer layer made of a substance different from that of the substrate is formed on a part of the substrate, and a thin film is formed on both the substrate and the buffer layer. Since the crystal grain boundaries are artificially formed by changing the in-plane orientation of the thin film formed on the substrate and the thin film formed on the buffer layer, the crystal grain boundaries can be easily integrated at any place with a high degree of integration. There is an effect that can be formed.

Further, by forming the oxide superconducting film as a thin film, the grain boundary junction of the oxide superconducting film can be formed at an arbitrary place on the substrate, so that the Josephson junction can be easily integrated. It can be manufactured at high cost, the degree of freedom in circuit design is improved, and the compatibility with the micro process is improved.

Further, the misalignment angle of the grain boundary junction can be controlled by adjusting the film forming conditions of the oxide superconducting film, so that the rotation angle of the grain boundary junction can be formed at a desired angle. It is possible to increase the critical current by making it smaller than 45 degrees.

By forming the ferroelectric film as a thin film, the grain boundary junction of the ferroelectric film can be formed independently at any place on the substrate.
An artificial grain boundary exhibiting the C effect can be formed independently, the resistance temperature characteristic and the like are improved, the degree of freedom in circuit design can be increased, and the degree of integration can be increased.

[Brief description of drawings]

FIG. 1 is an explanatory view showing an example of a method for manufacturing a Josephson junction according to an embodiment of the method for manufacturing an artificial grain boundary of the present invention.

FIG. 2 is a waveform diagram showing an X-ray diffraction pattern for explaining control of in-plane crystal orientation of an oxide superconducting film according to an example of the present invention.

FIG. 3 is an explanatory view showing another example of a method for manufacturing a Josephson junction, which is another embodiment of the method for manufacturing an artificial grain boundary of the present invention.

FIG. 4 is a waveform diagram of an X-ray diffraction pattern showing an in-plane crystal orientation of an oxide superconducting film according to another example of the present invention.

FIG. 5 is an explanatory view showing a method for producing an artificial grain boundary showing a PTC effect according to still another embodiment of the present invention.

FIG. 6 shows P obtained according to still another embodiment of the present invention.
It is a characteristic view which shows the resistance temperature characteristic of TC thermistor.

FIG. 7 is an explanatory diagram showing a conventional method for manufacturing a Josephson junction.

FIG. 8 is a schematic view showing natural grain boundaries in a conventional ceramic.

FIG. 9 is a characteristic diagram showing resistance temperature characteristics of a conventional PTC thermistor.

[Explanation of symbols]

1 Strontium titanate (001) substrate 2 Magnesium oxide buffer layer 3 (001) -oriented bismuth oxide superconducting film parallel to the [110] direction of the substrate 4a (001) -oriented parallel to the [100] direction of the substrate Bismuth oxide superconducting film

[Outside 3] Mass-type oxide superconducting film 5 Grain boundary junction 13 Barium titanate film of ferroelectric film having (001) orientation parallel to [110] direction of substrate 14 (001) orientation parallel to [100] direction of substrate Barium Titanate Film of Ferroelectric Film

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Koichi Hamanaka 8-1-1 Tsukaguchihonmachi, Amagasaki City Mitsubishi Electric Corporation Central Research Institute (72) Inventor Yukihisa Yoshida 8-1-1 Tsukaguchihonmachi, Amagasaki Mitsubishi Electric Central Research Institute Co., Ltd. (72) Inventor Masayuki Kataoka 8-1-1 Tsukaguchihonmachi, Amagasaki City Mitsubishi Electric Corporation

Claims (5)

[Claims] 1. A buffer layer made of a substance different from that of the substrate is formed on a part of the substrate, and a thin film is formed on both the substrate and the buffer layer, and the thin film formed on the substrate and the buffer. A method for producing an artificial grain boundary in which a crystal grain boundary is artificially formed by changing the in-plane orientation of a thin film formed on a layer. 2. A substrate made of either strontium titanate or magnesium oxide (001)
2. The method for producing an artificial grain boundary according to claim 1, wherein the surface is used as the substrate surface and either the other of strontium titanate or magnesium oxide is used as the buffer layer. 3. The method for producing an artificial grain boundary according to claim 1 or 2, wherein an oxide superconducting film is formed as a thin film. 4. The method for producing a Josephson junction according to claim 3, wherein the film forming conditions of the oxide superconducting film are adjusted to control the misalignment angle of the grain boundary junction. 5. The method for producing an artificial grain boundary according to claim 1 or 2, wherein a ferroelectric film is formed as a thin film.