JP3092204B2 - Superconducting element manufacturing method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a superconducting element of a superconducting application technology, and more particularly to a Bi-based oxide superconductor containing an alkaline earth metal as a pair of electrodes. The present invention relates to a superconducting element having a structure in which a weak coupling portion is provided.

[0002]

2. Description of the Related Art Some oxide superconductors discovered in recent years have a superconducting transition temperature exceeding liquid nitrogen temperature (77.3 Kelvin), which will greatly expand the field of application of superconductors. It became.

[0003] With regard to the superconducting element which is one of the practical applications, the oxide superconductor is divided into two parts, and the Josephson element and the oxide superconductor which are brought into slight contact again are made into a thin film, and a small constriction is formed. Conventionally, a bridge-type Josephson device and a Josephson device in which oxide superconductors are connected with a noble metal such as Au or Ag have been manufactured.

[0004]

Among the devices which have been conventionally manufactured, in a superconducting device having a crystal grain boundary as a weak coupling portion, a crystal grain boundary generated by chance in a superconductor thin film on a substrate is found. This portion is used as a weak coupling portion of the superconducting element, and it has been difficult to manufacture the superconducting element at an arbitrary location with good controllability. Furthermore, it has been difficult to simultaneously integrate and fabricate a plurality of elements on a substrate.

[0005] Further, as an example in which a crystal grain boundary is formed at a specific place and a superconducting element is formed, a bicrystal substrate is used as a base, and an oxide superconducting thin film is epitaxially grown on the base to form a crystal grain of the substrate. There is a superconducting element using a crystal grain boundary of an oxide superconductor thin film formed by reflecting a boundary.
However, this bicrystal base plate is obtained by laminating single crystals having different crystal orientations at a high temperature and a high pressure, cutting the single crystal into a base plate shape including a crystal grain boundary in a plane, and polishing it. It is difficult to fabricate the bicrystal substrate itself, and the epitaxial growth of the oxide superconducting thin film also requires a high technique.

The present invention relates to a method of manufacturing a superconducting element utilizing a crystal grain boundary as a weak coupling portion, wherein the weak coupling portion is formed at an arbitrary portion on a base without using a bicrystal substrate. The purpose is to provide.

[0007]

Means for Solving the Problems In order to form a crystal grain boundary at an arbitrary position in an oxide superconductor thin film formed on a substrate, a buffer layer covering the surface except for a part of the substrate is provided. One of the three methods of using the surface of the base as a seed crystal, forming a seed crystal serving as a crystal nucleus on the base, or covering the oxide superconductor with a cap seal layer is performed.

Further, the oxide superconductor thin film has a melting point
Heat recrystallization is performed as described above , and crystal grain boundaries are generated at specific locations.

[0009]

A buffer layer is provided on a substrate, a plurality of windows are formed on a portion of the buffer layer so that the surface of the substrate is exposed, and an oxide superconductor thin film containing Cu is formed thereon. When the conductor thin film is heated and recrystallized, the portion where the substrate and the superconductor thin film are in contact is crystallized by reflecting the crystal orientation of the substrate, so that a crystal grain boundary is formed in the middle region between the windows. You.

In addition, a plurality of seed crystals serving as crystal nuclei are formed on a substrate, an oxide superconductor thin film containing Cu is formed thereon, and thereafter, the oxide superconductor thin film is recrystallized by heating. When this is done, crystallization takes place reflecting the crystal orientation of the seed crystal, so that a crystal grain boundary is generated at an intermediate position between the seed crystals.

Further, a cap seal layer is deposited so as to cover the oxide superconductor thin film, and thereafter, the oxide superconductor thin film is heated and recrystallized. A temperature difference occurs between the contacting portion and the central portion, and a crystal grain boundary occurs at the central portion.

If the heating method is performed by a linear heating device, a laser beam heating device, or an electron beam scanning device during the heating and recrystallization, the temperature distribution at the time of heating can be controlled. It is preferable for production. Among these, the laser beam heating device could make the temperature distribution of the oxide thin film a distribution in which crystal grain boundaries are easily formed by performing focusing or defocusing by a lens. In addition, the heating method using the electron beam scanning device can easily change the temperature distribution of the heated portion on the base by electrical control. Further, other heating methods except for the electron beam scanning device can heat and recrystallize the sample in oxygen, sufficiently supply oxygen to the oxide superconductor, and are effective in improving superconductivity. Therefore, it is preferable. In addition, the wire heating device made of Pt or an alloy containing Pt can stably perform heat treatment without burning even in an oxidizing atmosphere.

Further, when a plurality of superconducting elements are manufactured on the same substrate by the above-described manufacturing methods, the characteristics of each element have small variations, and the elements can be manufactured at positions corresponding to the design. In addition, it shows good superconductivity even at a temperature of liquid nitrogen or higher, and shows a Josephson effect.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention aims at fabricating a crystal grain boundary at a specific location on a substrate in a superconducting element having a crystal grain boundary as a weakly bonded portion. The superconducting element is produced by heating and recrystallizing.

The superconducting element of the present invention shows its effect more remarkably, especially for the application of a superconducting element which requires integrating a plurality of superconducting elements on the same substrate.

Hereinafter, the present invention will be described in more detail with reference to specific examples. Embodiment 1 Embodiment Using an Electron Beam Scanning Apparatus FIG. 1 is a schematic diagram illustrating a first invention of the present invention. The substrate 2 was made of (100) SrTiO ₃ , and the substrate was kept at 300 ° C. by sputtering to obtain Ar
SrTiO _{3 serving} as the buffer layer 4 was deposited to a thickness of 200 nm with 100% gas and a power of 200 W. SrTiO ₃ deposited under these conditions becomes amorphous due to the low formation temperature. Thereafter, a part of the buffer layer 4 was removed by a photoresist and a chemical etching method, and a part of the base 2 was exposed to form a window 6. Next, a 123-based oxide superconductor, YBa2Cu, which is an oxide superconductor thin film 1, is formed on the entire surface of the substrate by RF magnetron sputtering.
3Ox was deposited at 680 ° C. to 300 nm. Next, the substrate was placed in an electron beam scanning device, and after evacuating to 2 × 10 ⁻⁵ Pa or less, the electron beam 5 was scanned over the filament, and a part of the substrate was heated to about 1000 ° C. and melted. . At this time, when the scanning portion of the linear electron beam 5 was gradually moved in a direction different from the scanning direction, recrystallized from the portion where the electron beam 5 passed. When this melted portion passes through the portion of the window 6 opened in the buffer layer 4, that is, the portion in contact with the base 2 and the oxide superconductor thin film 1, the oxide Crystallization of the conductor thin film 1 occurred epitaxially, and a crystal grain boundary 3 was formed near a window and an intermediate portion of the window. Since the scanning of the electron beam 5 can be easily controlled by an electric signal, the temperature distribution of the substrate 2 during the scanning can be set arbitrarily.

Embodiment 2 An embodiment using a laser beam heating device in an oxygen atmosphere. FIG. 2 is a schematic diagram illustrating a second invention of the present invention. The fused silica used in the base body 2, at 720 ° C. thereon, oxide as superconductor thin film, Bi-based oxide superconductor mainly including an oxide superconductor of 2212 phase _{(Bi 1-y Pb y)} 2 -Sr ₂ -Ca ₁ -Cu ₂ -O _x , where 0 ≦ y <0.5, where x is arbitrary, an oxide superconductor thin film having a thickness of 300 nm using an oxide powder target adjusted to deposit Was deposited. Subsequently, one atmosphere of oxygen was introduced into the vacuum vessel, and 950 ° C.
Heat treatment was performed for one hour to form a large number of seed crystals 8 having a diameter of several tens μm to several hundreds μm. Thereafter, oxide superconductors other than the crystal (seed crystal 8) at a specific portion were removed by a photoresist and a chemical etching method. Then, after removing the photoresist, an oxide superconductor thin film 1 was formed on the entire surface. Deposition, at 720 ° C., Bi-based oxide superconductor mainly including an oxide superconductor of 2212 phase _{(Bi 1-y Pb y)} 2 -Sr 2 -Ca 1 -Cu 2 -O x, ( where 0 ≦ y <0.5, x is arbitrary) by RF magnetron sputtering to 300 n
m. Next, the substrate 2 was placed in a laser beam heating device, and the substrate 2 was irradiated with the laser beam 7 at 1 atm of pure oxygen, and a part of the substrate 2 was heated to about 950 ° C. and melted.
At this time, when the laser beam 7 is narrowed down to a line by a lens and the laser beam 7 is gradually moved in a direction different from the line direction,
Recrystallization is performed from the portion where the laser beam 7 has passed. When this molten portion passes through the portion of the seed crystal 8 at the time of crystal growth, that is, the portion of the oxide superconductor initially crystallized and left on the base 2, it reflects the crystal orientation of the seed crystal 8. The crystallization of the oxide superconductor thin film 1 occurs epitaxially,
A crystal grain boundary 3 was formed in the vicinity of an intermediate portion between the adjacent seed crystal and the seed crystal. The scanning of the laser beam 7 was easily realized by mechanically controlling a mirror in the optical path of the laser.

Embodiment 3 Embodiment Using a Wire Heating Apparatus Using Pt as a Heater FIG. 3 is a schematic diagram illustrating a third invention of the present invention. A (100) MgO substrate was used for the substrate 2, and 720 ° C.
The oxide superconductor thin film 1 mainly has the following Tl
System oxide superconductor _{Tl 2 -Ba 2 -Ca 2 -Cu 3} -O x, ( where x is any) using an oxide powder target was adjusted so that is deposited, oxide thickness 300nm superconducting A body thin film 1 was deposited. Thereafter, a stripe-shaped groove was formed in the oxide superconductor thin film 1 by a photoresist and a chemical etching method. After removing the photoresist,
At 200C, a 200 nm yttrium stabilized zirconia (YSZ) thin film was deposited as a cap seal layer 10 by RF magnetron sputtering. Then Pt
The substrate 2 is placed in a wire heating container using the wire as the wire heating device 9, and the substrate 2 and the oxide superconductor thin film 1 are heated in one atmosphere of pure oxygen, and the oxide superconductor thin film 1 is re-heated. Crystallized. Heating of the substrate was around 930 ° C. At this time, when the linear heating device 9 is gradually moved in the groove direction (stripe direction) of the cap seal layer 10, recrystallization starts from the portion where the Pt heater has passed. At this time, since the temperature distribution is different between the portion in contact with the end of the cap seal layer and the central portion (the central portion becomes high temperature or the cooling rate is low), a crystal grain boundary 3 is formed in the central portion.

FIG. 4 is a schematic view showing an example of a superconducting element manufactured using the substrate of the second invention described above. This is what is called a grain boundary junction Josephson element, and is an example in which a large number of a plurality of Josephson elements are formed on the same substrate. Each device formed a superconducting quantum interference system, and each device showed almost no variation in characteristics, and exhibited good superconducting device characteristics even at liquid nitrogen temperature.

As described above, upon heating and recrystallization, as a heating method, a linear heating device, a laser beam heating device,
When using an electron beam scanning device, the temperature distribution during heating can be controlled, and thus there is an effect that a crystal grain boundary can be formed at an arbitrary position. Among these, the laser beam heating device can condense or defocus by a lens to make the temperature distribution of the oxide thin film a distribution in which crystal grain boundaries are easily formed, and heating by an electron beam scanning device. The method has an effect that the temperature distribution can be easily changed by electric control. Further, other heating methods except for the electron beam scanning device can heat and recrystallize the sample in oxygen, sufficiently supply oxygen to the oxide superconductor, and are effective in improving superconductivity. . In addition, the wire heating device using Pt or an alloy containing Pt has an effect of performing a stable heat treatment without burning out even in an oxidizing atmosphere.

When a superconducting element was manufactured by using the above-described manufacturing methods, good superconducting characteristics were exhibited even at a temperature of liquid nitrogen or higher, and a Josephson effect was obtained.

One superconducting application at present is a superconducting quantum interferometer having a Josephson element as a constituent element. The superconducting device of the present invention operates as a Josephson device at the temperature of liquid nitrogen. Using this device, it has become possible to construct a superconducting quantum interferometer that operates at the temperature of liquid nitrogen. This superconducting quantum interferometer responds with extremely high sensitivity to magnetic fields, and can be applied to magnetic measurements such as biomagnetism measurement and geomagnetism measurement, as well as computer memory and computer logic using switching elements with low power consumption. . In particular, in the field of biomagnetism measurement, the neural activity of the brain, which could not be measured non-invasively conventionally, can be non-invasively extracted as a magnetic signal, so that it has attracted attention not only in the field of basic medicine but also in the field of clinical medicine.

In these respects, the practical effects of the present invention are large in fields such as biomagnetism measurement applications in basic medicine and clinical medicine fields, computer applications using switching elements with low power consumption, and electronic device applications. is there.

[0024]

According to the present invention, there is provided a method for manufacturing a superconducting element in which an oxide superconductor containing Cu on a substrate is recrystallized by heating, and a crystal grain boundary generated at that time is used as a weak coupling part. In order to form grain boundaries at predetermined locations, a buffer layer covering the surface of the substrate is formed, a window is provided on a portion of the buffer layer to expose the substrate, and an oxide superconductor is further formed thereon,
The substrate is recrystallized by heating, or a seed crystal serving as a crystal nucleus is formed on the substrate, an oxide superconductor is formed thereon, and the substrate is recrystallized by heating or oxidized on the substrate. Forming a material superconductor, depositing a cap seal layer so as to cover the oxide superconductor, and heating and recrystallizing the substrate, the effect that a grain boundary can be produced at a specific portion on the substrate There is.

[Brief description of the drawings]

FIG. 1A is a perspective view illustrating a manufacturing method according to an embodiment of the first invention; FIG. 1B is a cross-sectional view illustrating a manufacturing method according to an embodiment of the first invention;

FIG. 2A is a perspective view illustrating a manufacturing method according to an embodiment of the second invention; FIG. 2B is a cross-sectional view illustrating a manufacturing method according to the embodiment of the second invention;

FIG. 3A is a perspective view illustrating a manufacturing method according to an embodiment of the third invention; FIG. 3B is a cross-sectional view illustrating a manufacturing method according to the embodiment of the third invention;

FIG. 4 is a perspective view showing an example of a grain boundary junction Josephson device manufactured according to the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Oxide superconductor thin film 2 Substrate 3 Crystal grain boundary 4 Buffer layer 5 Electron beam 6 Window 7 Laser beam 8 Seed crystal 9 Wire heating device 10 Cap seal layer

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-2-271913 (JP, A) JP-A-2-260475 (JP, A) JP-A-2-258696 (JP, A) JP-A-2-271 279597 (JP, A) (58) Fields studied (Int. Cl. ⁷ , DB name) H01L 39/24 H01L 39/22 H01L 39/00

Claims (3)

(57) [Claims] 1. A buffer layer having at least two openings is formed on a base, an oxide superconductor containing Cu is formed on the buffer layer, and a line is formed in a direction crossing a line connecting the openings. A method for manufacturing a superconducting element, comprising: performing a heating method to recrystallize the oxide superconductor containing Cu. 2. A seed crystal serving as at least two crystal nuclei is formed on a base, an oxide superconductor containing Cu is formed on the base including the seed crystal, and a line connecting the seed crystals is formed. A method of manufacturing a superconducting element, comprising applying linear heating in a transverse direction to perform recrystallization treatment of the oxide superconductor containing Cu. 3. Cu on the substrate except for a part of the substrate surface
Is provided, a cap sealing layer is further deposited so as to cover the oxide superconductor containing Cu and the surface of the substrate , and a wire heating method is applied.
A method for manufacturing a superconducting element, comprising recrystallizing an oxide superconductor containing u.