JP3149460B2 - Method of manufacturing Josephson device - Google Patents

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 Josephson device, which is one of superconducting applied technologies.

[0002]

2. Description of the Related Art Some oxide superconductors discovered recently have a superconducting transition temperature of liquid nitrogen temperature (77.3K).
And greatly expanded the field of application of superconductors. Various manufacturing methods have been devised and tested for the Josephson device, which is one of the practical applications of this metal oxide superconductor. A break-type Josephson device in which the oxide superconductor is divided into two parts and brought into slight contact again, utilizing the so-called grain boundary junction, which actively utilizes the phenomenon of grain growth that occurs when producing an oxide superconductor film Josephson devices have been produced as prototypes, but they have problems with reproducibility and are far from practical. In a tunnel-type Josephson junction, it is necessary to sandwich an extremely thin (about several nm) insulating film with a superconductor, and a device using a metal oxide superconductor, which is difficult to form a stable insulating film, cannot be manufactured. Extremely difficult.

On the other hand, a bridge-type Josephson junction, which is a weak-coupling Josephson junction, is a structure in which two superconducting portions are connected by a minute bridge portion, has a two-dimensional structure, and has a normal etching process. Therefore, the manufacturing process is simple and simple, and furthermore, there are advantages such as possibility of monolithic formation with other electronic devices, and the practicality is high.

[0004]

However, in the bridge-type Josephson junction, the dimensions of the bridge portion need to be approximately the coherent length (several nanometers) in principle, and the method and accuracy of processing to the coherent length are required. Is an issue.

An object of the present invention is to provide a method of manufacturing a Josephson element which has solved such processing accuracy.

[0006]

In the method of manufacturing a Josephson device according to the present invention, the conventional problems have been overcome by irradiating a bridge portion formed by etching a metal oxide superconducting thin film with ultraviolet rays. .

[0007]

According to the method of manufacturing a Josephson device of the present invention, a bridge portion is formed by etching and then irradiated with ultraviolet rays.
The present inventors have clarified in Japanese Patent Application No. 2-216885 or the like that oxygen vacancies are generated in the metal oxide superconducting thin film by ultraviolet irradiation, and the superconducting properties are deteriorated or disappear. As a result of the intensive efforts of the present inventors, it has been found that the effect of this ultraviolet irradiation gradually affects the inside from the film surface due to an increase in the irradiation amount (irradiation intensity × irradiation time), and the irradiation amount is accurately adjusted. It was also found that if controlled, the superconducting properties deteriorate from the film surface to the desired depth. Therefore, by selectively deteriorating or eliminating the superconducting characteristics only by the effective thickness of the bridge portion, a bridge-type Josephson junction can be produced with good reproducibility even with relatively low etching accuracy.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the Josephson device of the present invention, a metal oxide superconducting thin film is formed on a substrate, and the thin film is etched to form a schematic shape of a bridge type Josephson device.

The substrate used in the present invention is, for example, M
Normal substrate materials such as gO can be applied.

For the metal oxide superconducting thin film formed in the present invention, for example, sputter vapor deposition, CVD vapor deposition, electron beam vapor deposition, resistance heating vapor deposition, etc. are applied, but the composition control of the metal oxide superconducting thin film is easy. Therefore, sputter deposition is preferred.

Further, the etching method of the present invention includes:
For example, a normal method such as ion beam etching can be sufficiently used.

The metal oxide superconducting thin film used in the present invention may be any material as long as its superconducting properties change when irradiated with ultraviolet light. For example, an AB—Cu—O-based composite compound (where A is at least one of Sc, Y, La, and La series elements (atomic numbers 57, 59 to 60, and 62 to 71))
Species, B is at least one of Group IIa elements such as Ba and Sr
Species, and the concentration of both A and B elements and Cu element is 0.5 ≦
(A + B) /Cu≦2.5 is satisfied), Bi−
Sr-Ca-Cu-O-based composite compound, Bi-Sr-Ca-
A compound in which a part of Sr atoms in a Cu-O-based composite compound is substituted with Pb, a Tl-Ba-Ca-Cu-O-based composite compound, or a Ba in a Tl-Ba-Ca-Cu-O-based composite compound A copper-based composite oxide or a non-copper-based composite oxide such as a compound in which some of the atoms are substituted with Pb is provided. However,
Of course, in these superconducting materials, the operating temperature of the manufactured Josephson element changes as each superconducting transition temperature changes.

Ultraviolet rays are selectively applied only to the bridge portion of the Josephson element roughly formed by etching to make this bridge portion non-superconductive. The Josephson element of the present invention is characterized in that the bridge portion is irradiated with ultraviolet rays. Irradiation of a superconductor with an energy beam causes a change in superconductivity, as described in Japanese Patent Application No. 2-216885.
However, when an energy ray having a higher energy than ultraviolet rays is irradiated, even if the irradiation amount is controlled, the energy ray reaches the inside of the superconducting thin film, and the superconducting property of the irradiated part cannot be controlled. Therefore, the superconductivity can be controlled by controlling the irradiation amount only in the case of ultraviolet rays having low energy of the irradiated energy rays. The wavelength range of ultraviolet light applicable to the present invention is near ultraviolet light of 400 to 300 nm or far ultraviolet light of 300 to 190 nm.

An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 shows one step of a method for manufacturing a Josephson device according to one embodiment of the present invention. Here, the metal oxide superconducting thin film 12 is formed on the substrate 11 by, for example, sputtering. Next, as shown in FIG. 1, two electrode portions 13 and a bridge portion 14 connecting them are formed by using a method such as photolithography and dry etching.
To form And finally, for the bridge part 14,
Irradiate with ultraviolet light.

The superconductivity is deteriorated from the surface portion of the bridge portion 14 by the ultraviolet irradiation, and the effective thickness of the bridge portion can be controlled. Then, by appropriately adjusting the irradiation amount, the effective bridge thickness can be extremely reduced to about the coherent length, whereby the bridge-type Josephson effect appears.

Bridge part 1 when manufactured by etching
The actual width of 4 may be about 10 μm or less, which can be sufficiently realized by a normal dry etching process, and does not require ultra-high precision processing such as a focused ion beam. Also,
The ultraviolet irradiation area may be applied to the whole or a part of the bridge portion 14. Therefore, it is not necessary to perform exposure with high precision using a photomask or the like, and it is sufficient to place a metal mask on the sample. is there.

In order to further understand the effects of the present invention,
A specific embodiment will be described with reference to FIG.

Example 1 An MgO single crystal was used as a substrate 11, and a metal oxide superconducting thin film 12 was formed on a (100) plane thereof by a high-frequency planar magnetron sputtering. In sputtering, sintered BiSrCaCuO powder was used as a target. The sputtering conditions were as follows: Ar, O ₂ mixed gas pressure 0.5 Pa;
Gas mixture ratio Ar: O ₂ = 1: 5, sputtering power 150
W, the sputtering time is 10 minutes, and the thickness of the thin film is 110 nm. The temperature of the substrate 11 at the time of sputtering is 580 ° C.
I made it. The superconducting transition temperature of the resulting thin film 12 was 80K. The surface of the thin film 12 had sufficient flatness to form a Josephson junction.

On the surface of the metal oxide superconducting thin film 12,
A negative photoresist (OMR) was spin-coated. width,
Photomask with bridge pattern of 10μm in length
Exposure using a mask, developing and etching
Was formed on the film 12. Etching is argon ion
Approximately 600 μA / cm using a beam etching device ^Two
Etching was performed for about 25 minutes at an ion current density of FIG.
A pattern of metal oxide superconducting thin film like
Was. After etching, the remaining resist film on the surface
Oxidized by elementary plasma and removed.

Next, ultraviolet irradiation was performed. For the light source,
The sample was set in reduced pressure helium gas using a 160 W low pressure mercury lamp to prevent ozone generation around the sample. A metal mask is placed on the sample, and only the bridge portion 14 is irradiated with ultraviolet light, and ultraviolet light irradiation is performed for about 1 hour, thereby completing the device manufacturing process.

When a constant current is passed between the electrode portions 13, the voltage at both ends is measured, and while observing the voltage-current characteristics, a microwave of about 10 GHz is applied to the bridge portion. At a temperature lower than the transition temperature, when the current was increased or decreased, a stepwise voltage change of about 20 μV, a so-called Shapiro step, was observed. From this, it was confirmed that a Josephson junction was formed by the present manufacturing method.

In the above embodiment, the metal oxide superconducting thin film 1
2, a Bi-Sr-Ca-Cu-O superconducting thin film was used. However, the present invention is not limited to this type, and AB-Cu-
The present invention was similarly effective when the —O composite compound was used. Here, A is at least one of Sc, Y, La, and La series elements (atomic numbers 57, 59 to 60, 62 to 71), B is at least one of Group IIa elements such as Ba and Sr, and The concentration of the A, B and Cu elements is 0.
If 5 ≦ (A + B) /Cu≦2.5 is satisfied, there will be some difference in the superconducting transition temperature of the prepared thin film, but basically there is no change in its effectiveness for the present invention. Further, B
Some of the Sr atoms in the i-Sr-Ca-Cu-O compound are converted to Pb
Or Tl-Ba-Ca-C
The present invention was similarly effective when a compound in which a part of Ba atoms in the u-O compound or Tl-Ba-Ca-Cu-O compound was substituted with Pb was used.

[0023]

According to the method for manufacturing a Josephson device of the present invention, a metal oxide superconducting thin film is processed by etching and then irradiated with ultraviolet rays. By controlling the amount of ultraviolet irradiation, a Josephson element having good characteristics can be manufactured with good reproducibility without requiring processing accuracy of about several nm, which is conventionally required for manufacturing a normal bridge type Josephson junction.

The Josephson element is a very important component in an ultra-high-performance microwave mixer, an ultra-sensitive magnetic field measuring device, and the like.
Since the discovery of a material having a higher transition temperature can be expected in the future, the industrial value of the present invention is high.

[Brief description of the drawings]

FIG. 1 is a perspective view showing one step of a method for manufacturing a Josephson device according to an embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Substrate 2 Metal oxide superconducting thin film 3 Electrode part 4 Bridge part

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-1-161789 (JP, A) JP-A-1-125002 (JP, A) JP-A-1-220875 (JP, A) JP-A-1- 257380 (JP, A) (58) Fields studied (Int. Cl. ⁷ , DB name) H01L 39/22-39/24 H01L 39/00

Claims (3)

(57) [Claims] After a metal oxide superconducting thin film is formed on a substrate, the metal oxide superconducting thin film is etched to form two electrode portions and a minute bridge portion connecting the two electrode portions. Ultraviolet light with a wavelength of 190 to 400 nm
Irradiating a line, the metal oxide constituting the bridge portion
Method of manufacturing a Josephson device characterized by causing oxygen deficiency in the surface of the superconductive thin film 2. The superconducting metal oxide thin film is AB-Cu
The method for producing a Josephson device according to claim 1, wherein the method is a —O composite compound. Where A is Sc,
Y, La, and La series elements (atomic numbers 57, 59 to
60, 62 to 71), B is at least one of Group IIa elements, and the concentration of both A and B elements and Cu element is 0.5 ≦ (A + B) /Cu≦2.5. 3. The method according to claim 1, wherein the metal oxide superconducting thin film is Bi-Sr-C.
an a-Cu-O-based compound, a compound in which part of the Sr atoms in the Bi-Sr-Ca-Cu-O-based compound is substituted with Pb,
1-Ba-Ca-Cu-O-based compound or Tl-B
Part of Ba atoms in a-Ca-Cu-O-based compound is converted to Pb
Characterized in that it is any of the compounds substituted with
A method for manufacturing a Josephson device according to claim 1.