JPH02114678A - Superconductive element - Google Patents

Abstract

PURPOSE:To enable the formation of a Josephson junction precisely at a specified position by a method wherein a superconductive element of this design is constituted in such a structure that two bank sections are electrically connected with each other by a bridge of a thin film whose thickness is smaller than that of the bank and which is formed of a material which contain the same composition as a metal oxide superconductive thin film. CONSTITUTION:A superconductive element has a structure that two bank sections 4a and 4b formed of a metal oxide superconductive thin film 2 on a substrate 1 are connected with each other with a bridge 3 formed of a material which contains the same composition as the metal oxide thin film 2, where the thickness of the bridge 3 is smaller than that of the bank sections 4. And, the superconductive characteristics of the bridge 3 small in thickness can be observed from the outside through the bank sections 4a and 4b. Therefore, a Josephson junction is formed inside the bridge 3, so that the junction can be reproducibly formed at an optional position and consequently a superconductive element, which is provided with a Josephson junction possessed of a specified critical current value and formed at any position, can be easily manufactured.

Description

[Detailed Description of the Invention] Industrial Application Field The present invention relates to a superconducting element using a superconductor.
In particular, it relates to superconducting elements using oxide superconductors.

Conventional technology As high-temperature superconductors, niobium nitride (NbN) and germanium niobium (NbsGe) are used as mu-16 type binary compounds.
) were known. Many Josephson devices using these materials have also been studied. The superconducting transition temperature of these materials was at most 24°. On the other hand, perovskite-based ternary compounds are expected to have even higher transition temperatures, and Ba-La-Cu-0-based high-temperature superconductors have been proposed (J. (Zetshrif'tftfr phy
sik B) -Condensed Matter
64189-193 (1986)).

Furthermore, it has recently been proposed that the Y-Ba-Cu-0 system is a higher temperature superconductor (M., Wu et al., Physical Review Letters).
Review Letters) Vol, 5B,
No. 9.908-910 (198a)].

The details of the superconducting mechanism of Y-Ba-Cu-0 materials are not clear, but the transition temperature may be higher than the liquid nitrogen temperature, making them a high-temperature superconductor compared to conventional binary compounds. However, more promising properties are expected.

In addition, very recently, Bi-Sr-Ca-Cu-0 system and Tl-Ba-Ca-(ju-0 system 1oO°K
High-temperature superconductors have also been discovered with critical temperatures exceeding .

Problems to be Solved by the Invention However, when a superconducting device is put into practical use using the above-mentioned oxide high-temperature superconducting thin film, the fact that the coherence length is extremely short, a few nanometers, causes problems such as film non-uniformity and crystal grains. This is the main reason why it is extremely difficult to manufacture.

This means that when creating a weakly coupled Josephson device,
It is necessary to make the bridge length of the weak coupling part about the same as the coherence length, and in reality, such a nanobridge structure is difficult to fabricate using oxides and has not been realized. Further, a strip-shaped Josephson element using grain boundary junctions has been proposed, but the element dimensions are large and it is difficult to fabricate Josephson junctions at predetermined positions with high precision.

Means for Solving the Problems The superconducting element of the present invention comprises two bank portions made of a metal oxide superconducting thin film formed on a substrate, and a material containing the same composition as the metal oxide superconducting thin film. It is characterized by having a structure in which the two bank parts are electrically connected by a thin bridge part that is thinner than the film thickness of the bank part.

When the material of the metal oxide superconducting thin film is a metal oxide superconductor containing a copper element, or when the metal oxide superconductor containing a copper element is an A-B-Cu-0 composite compound. Also included.

Here, A is Sc, Y, La, and La series elements (atomic numbers 57 to 71, excluding 57.61.62)
At least one of them, B is IIa such as Ba and Sr.
At least one group element, human, B element and Cu
The concentration of the element is.

Further, the metal oxide superconductor containing the copper element contains Bi, and also contains n such as Pb, Sr, Ca, etc.

Including cases where at least one element among group elements is included,
Furthermore, cases where the metal oxide superconductor containing the copper element contains TI and at least one element among Pb or Group IIa elements such as Ba and Ca are also included.

Furthermore, the material of the metal oxide superconducting thin film is Ba and B.
It also includes cases where it is a composite oxide superconductor containing i.

As a method for manufacturing a superconducting element of the present invention, an etching mask is formed on a metal oxide superconducting thin film formed on a substrate using photolithography technology except for the upper part corresponding to the bridge part, and then an inert film is formed on the metal oxide superconducting thin film formed on a substrate. A method is provided in which a portion of the metal oxide superconducting thin film corresponding to the bridge portion is etched by irradiating gas ions to form a bridge portion, and then the etching mask is removed.

Alternatively, a metal oxide thin film formed on a substrate is etched in the portion corresponding to the bridge portion using photolithography technology and dry etching technology to reduce the film thickness, and then heat treated in an oxygen atmosphere. Then, a method is used in which the metal oxide thin film is made into a metal oxide superconducting thin film.

Operation In carrying out the present invention, the bridge portion, which is thinner than the bank portion and is connected to the bank portion that becomes the superconducting electrode consisting of two metal oxide superconducting thin films, has a larger current density due to the thinner film thickness. , the grain boundaries contained in the bridge portion, which can be formed precisely at a predetermined location, become a Josephson junction, which can be observed from an external system9. It becomes possible to create a Josephson junction with high precision and good reproducibility at the position of .

Furthermore, by controlling the film thickness of the bridge portion, the critical current value of the element can be adjusted.

The material for the metal oxide superconducting thin film is a metal oxide superconductor containing copper, containing an A-Cu-0 composite compound or Bi, and containing at least one element among Pb or Group IIa elements. material or contains T4 and Pb
A similar effect can also be seen with materials containing Group IIa elements. In addition, as a material for metal oxide superconducting thin films,
A similar effect can be obtained with a complex oxide superconductor containing Ba and Bi.

Next, in carrying out the method for manufacturing a superconducting element of the present invention, the metal oxide superconducting thin film is irradiated with inert gas ions such as a person using an etching mask to reduce the thickness of the metal oxide superconducting thin film only in the portion corresponding to the bridge. The method for forming the bridge portion not only allows the bridge to be formed at any position with high precision, but also allows the dimensions of the bridge portion to be shortened. In addition, it was previously thought that ion irradiation would damage the metal superconducting thin film and impair its superconducting properties, but as a result of detailed study by the inventors, they found that ion irradiation does not cause damage in the case of inert gas. It was found that the receiving layer was only a small part of the surface layer, and it was discovered that forming a bridge portion by ion irradiation with an inert gas such as Mur is an extremely effective means for forming weakly bonded junctions. In addition, grain boundaries included in the bridge portion were selectively etched by irradiation with inert gas ions, and grain boundary bonding characteristics were observed in some cases.

Furthermore, in carrying out the second manufacturing method, the method of etching the metal oxide thin film using photolithography technology and dry etching technology to form the bridge portion is as follows:
This is to prevent water-sensitive metal oxides from being damaged. Further, by subsequently heat-treating in oxygen, the metal oxide thin film changes to a crystal structure exhibiting superconductivity, and the effect of removing damage during processing is observed. Furthermore, in heat treatment in oxygen at a higher temperature, growth of crystal grains in the metal oxide superconducting thin film was observed, and an effect of selectively forming grain boundaries in the thinned bridge portions was observed. Therefore, in the manufacturing method of the present invention, grain boundary junctions with little damage can be formed precisely at arbitrary positions by photoprocessing and dry etching technology.

Embodiment FIGS. 1 and 2 are a perspective view and a sectional view showing an embodiment of the superconducting element of the present invention.

The superconducting element of the present invention has a structure in which two bank parts 4a and 4b made of a metal oxide superconducting thin film 2 on a substrate 1 are connected by a bridge part 3 made of a material containing the same composition as the metal oxide thin film 2. have. The film thickness of the bridge portion 3 is thinner than that of the bank portion 4. The superconducting element of the present invention is a device whose purpose is to observe the superconducting characteristics of the thinned bridge portion 3 from the outside through the two bank portions 41L and 4b. Therefore, since the Josephson junction is formed inside the bridge portion 3, it is possible to form the junction at any desired location with good reproducibility.

Next, specific examples will be described together with a method for manufacturing a superconducting element of the present invention.

FIG. 3 shows a process diagram showing an embodiment of the first manufacturing method of a superconducting element according to the second invention. First, MgO (1o
o ) as a metal oxide superconducting thin film 2 on a plane substrate 1,
A dBa2Cu50y thin film was deposited (Figure 3(a)).

Deposition was performed by RF planar magnetron sputtering using GdBIL2Cu4,50y as a target.
The test was carried out in a mixed gas atmosphere of argon and oxygen. The substrate temperature was e o O'C, and the film thickness was 0.6 μm.

Next, after patterning the device in the lateral direction using photolithography and argon ion milling, the metal oxide superconducting thin film 2 is patterned using photolithography, excluding only the bridge-equivalent portion 6 with a length of 1 μm. An etching mask 6 was formed (FIG. 3(b)). The etching mask 5 is made of negative resist with a thickness of 0.8 μm.
Made thick. This is etched by ion irradiation to form the bridge portion 3 (FIG. 3(C)). Red ion irradiation uses a Kaufmann type ion source and gas pressure I
The test was carried out at X10 Torr and an acceleration voltage of 600 to 1 Kv. Etching speed is approximately 25 nm/W for GBCO thin film.
In negative resist, it was about aonm/min. The etching film thickness of the bridge portion 3 was set to 0.3 μm. after that,
The remaining part of the etching mask 5 was removed by ashing using oxygen plasma, and the bank portion 4 was exposed to produce a superconducting element (FIG. 3(d)). Oxygen pressure is I Tor
It was set as r.

Figure 6 shows the current-voltage characteristics of the prototype superconducting element. Weak coupling characteristics as shown in the figure were confirmed.

Furthermore, as the film thickness of the bridge portion 3 (FIG. 2) becomes thinner, the critical current value of the device decreases, confirming that the critical current can be controlled by controlling the film thickness. In FIG. 6, the bridge section 3
For a superconducting element with a film thickness o of 16 μm, f = 4.8
The current-voltage characteristics when irradiated with GHz microwave are shown. As shown in the figure, ΔV=f−h/e (h is a blank constant of 6.63×10 J, s.

Voltage steps (Shapiro steps) at intervals of about 20 μV given by a direct charge of 1.60×10 G) were observed, and it was confirmed that a Josephson junction was formed.

Next, an embodiment of the second method for manufacturing a superconducting element according to the third invention will be described using the process diagram shown in FIG. An mgo (1oo) plane is used as the substrate 1, and Bi-Sr is deposited on it.
-(a -Cu -0(7) Metal oxide thin film 12 is R
The film was deposited to a thickness of approximately 0.0 μm by F magnetron sputtering (FIG. 4 (IL)). The composition of the metal oxide thin film 12 deposited at a substrate temperature of 200°C in an argon and oxygen mixed atmosphere is Bi:Sr:Ca:Cu=1:1:1.
: It was 2. This thin film 12 had a flat surface, but did not exhibit superconductivity even when cooled to 4.2K.

Next, after forming the lateral pattern of the element (shape of the bank part, etc.) by photoprocessing and sputter etching,
By photo process and OF4 reactive ion etching
) A 5i02 etching mask 15 was formed on the surface of the metal oxide 12 (FIG. 4(b)). Etching mask 1
6 has a thickness of 0.5 μm, and the bridge equivalent portion 6 has a width of 2 μm.
The structure was completely removed. Next, this was etched by irradiating it with argon ions 17 to make the film thickness of the bridge portion 3 0.3 μm (FIG. 4(C)). Next, C.F.
The etching mask 16 was removed by 4-reactive etching (FIG. 4(d)). Finally, in an oxygen atmosphere,
A heat treatment was performed at 890°C for 20 minutes and at 870'C for 6 hours to form a metal oxide superconducting thin film 2, thereby producing a superconducting element (FIG. 4(e)). According to SICM observation, the prepared sample has a rock plate shape with crystal grains of several tens of micrometers, with grain boundaries of 13
It was confirmed that 1 to 2 pieces were included in the bridge portion 3 with good reproducibility. Although the mechanism of this phenomenon is not known in detail, it is probably due to the difference in film thickness between the metal oxide thin film 12 in the bank part 4 and the bridge part 3 that the level difference affects the crystal growth, causing the grain boundaries 13 to form in the bridge part. It is thought that it may be possible to do it in 3. The fabricated superconducting element is shown in Figs.
It showed the same characteristics as shown in the figure, confirming that a good Josephson junction was formed. This bonding was thought to be due to grain boundaries 13.

In addition, in the description of the above embodiment, Mg0 (100
) surface was used, but the invention is not limited to this. Also,
As the metal oxide superconducting thin film 2, Gd-Ba-Cu-
0 thin film and Bi-Sr-Ca-Cu-0 thin film are given as examples, but the present invention is not limited thereto. for example,
A metal oxide superconductor containing copper element, Mu-B-Cu-
0 complex compound (herein, Sc, Y, La and LtL series elements (atomic number 57-71, however, 57,
61. 62), and B is B
At least one of group elements such as a, Sr, etc., and A and B elements and Cu, Bi-Pb-5r-Ca
-Cu-0 superconductor and other superconductors, Tl-Ba -C
u-0, Tl-Ba-Ca-Cu-0°Tl-Pb −
Contains TI such as Ba-Ja-Cu-0 and at least one of Pb or group ■ elements such as Ba and Ca.
A similar effect was obtained with superconductors containing seed elements. Furthermore, Ba-Pb-Bi-0, Ba--Bi-
0.

The inventors have confirmed that similar effects can be obtained with complex oxide superconductors containing Ba and Bi, such as Ba-Rb-Bi-0.

Furthermore, in the description of the embodiment of the method for manufacturing a superconducting element of the present invention, argon is used as the inert gas ion 7 used for ion irradiation, but the invention is not limited to this, and any inert gas may be used. It's okay. Further, although a negative resist is used as the etching mask 5, the present invention is not limited to this, and any material may be used as long as it has a masking effect during etching by inert gas ion irradiation.

Furthermore, in the description of the embodiment of the second manufacturing method of a superconducting element according to the present invention, etching of the bridge-corresponding portion 6 was carried out by irradiating argon ions 17, but this is not limiting. The inventors have confirmed that similar effects can be obtained using dry etching such as reactive ion etching. Although 5i02 was used for the etching mask 16, any material may be used as long as it can be used as a dry etching mask. Therefore, it goes without saying that any method may be used to remove the etching mask 15.

Further, although an example has been described in which the metal oxide thin film 12 does not exhibit superconductivity, it is clear that it may exhibit superconductivity.

In addition, in the description of the embodiments of both methods of manufacturing a superconducting element of the present invention, before forming the bridge portion 3 by etching,
Although it has been described that the elements such as the bank portion 4 are patterned in the horizontal direction, the present invention is not limited to this, and it is obvious that the same effect can be obtained even if the order is reversed.

Effects of the Invention In carrying out the superconducting device of the present invention, it has become possible to easily fabricate a superconducting device having a Josephson junction with a predetermined critical current value at any position, which was previously considered difficult. , its practical value is great.

In carrying out the method for manufacturing a superconducting element of the present invention, since etching by inert gas ion irradiation is used, short micron-submicron junctions can be easily formed, and additional etching is not required. Since this is possible, it becomes possible to adjust the critical current value downward, which has great industrial value.

In addition, in carrying out the method for manufacturing other superconducting elements of the present invention, processing damage can be improved or prevented by heat-treating the metal oxide thin film after processing to make it a superconducting thin film. It is now possible to selectively form fine Josephson junctions in predetermined locations even on metal oxide thin films that have been considered difficult to process, and where it is difficult to obtain a flat surface, and this has enormous industrial value.

[Brief explanation of the drawing]

1 and 2 are perspective views and cross-sectional views showing one embodiment of the superconducting element of the present invention, and FIG. 3 is a cross-sectional view of process steps showing an example of the first manufacturing method of the superconducting element of the present invention. 4 are process step cross-sectional views showing an example of the second manufacturing method of a superconducting element according to the present invention. DESCRIPTION OF SYMBOLS 1...Substrate, 2...Metal oxide superconducting thin film, 3...Bridge part, 4...Bank part, 5, 15...・・Etching mask, 7・・
...Inert gas ion, 12...Metal oxide thin film. Name of agent: Patent attorney Shigetaka Awano and 1 other person
*Ft 2-Eatable Distillation AT Trend JL Pingfu 3--Bridge 忤Fig. m-etching mask/6 Figure reduction diagram Procedure amendment form) 1 Display of case 1986 Patent application No. 268484 Name of the invention Person who makes corrections to superconducting elements Relationship to the case Patent application
Colonel Tokoro 1006 Kadoma, Kadoma City, Osaka Prefecture
(582) Akio Tanii, Representative of Matsushita Electric Industrial Co., Ltd.

Claims (1)

[Scope of Claims] (1) Two bank portions made of a metal oxide superconducting thin film formed on a substrate, and a thin film made of a material containing the same composition as the metal oxide superconducting thin film, and the A superconducting element having a structure in which the two bank parts are electrically connected by a bridge part that is thinner than the film thickness of the bank part. (2) The superconducting element according to claim 1, wherein the material of the metal oxide superconducting thin film is a metal oxide superconductor containing an element of copper. (3) As a metal oxide superconductor containing copper element, A-B
The superconducting element according to claim 2, characterized in that a -Cu-O composite compound is used. Here, A is at least one of Sc, Y, La, and La series elements (atomic numbers 57 to 71, but excluding 57, 61, and 62), and B is at least one of IIa group elements such as Ba and Sr. 1 type, and the concentration of elements A, B and Cu element is 0.5≦(A+B)/Cu≦2.5. (4) The metal oxide superconductor containing the copper element contains Bi and at least one element selected from group IIa elements such as Pb, Sr, and Ca. The superconducting element according to item 2. (5) Claims characterized in that the metal oxide superconductor containing the copper element contains Tl and at least one element selected from Pb and group IIa elements such as Ba and Ca. The superconducting element according to item 2. (6) The material of the metal oxide superconducting thin film is Ba and Bi.
The superconducting element according to claim 1, which is a composite oxide superconductor containing: (7) After forming an etching mask on the metal oxide superconducting thin film formed on the substrate except for the upper part corresponding to the bridge part using photolithography technology, inert gas ions are irradiated to the bridge part. Manufacturing a superconducting element according to claim 1, wherein the superconducting element is manufactured by etching the metal oxide superconducting thin film in a corresponding portion to form a bridge portion, and then removing the etching mask. Method. (8) The metal oxide thin film formed on the substrate is thinned by etching the portion corresponding to the bridge portion using photolithography technology and dry etching technology, and then heat-treated in an oxygen atmosphere. 2. The method of manufacturing a superconducting element according to claim 1, wherein the metal oxide thin film is a metal oxide superconducting thin film.