JPH065930A - Josephson junction element and manufacture thereof - Google Patents

Abstract

(57) [Summary] (Corrected) [Objective] To provide a Josephson junction device with good performance that enables easy and precise microfabrication of the junction portion, and a manufacturing method thereof. [Structure] The normal conductor layers 12 and 12 'and the superconductor layers 13 and 13' are sequentially laminated on a substrate 11, and a photoresist layer is formed thereon so that the superconductor layer in a predetermined region is exposed. After etching, the metal vapor is supplied from the direction inclined at a predetermined angle to the photoresist side with respect to the normal to the superconductor layer surface, leaving a region on the superconductor layer extending over a predetermined width from the etching end face of the photoresist layer. The metal layers 14 and 14 'are vapor-deposited on the other regions, the metal layer is used as a mask to form a groove 15 penetrating the superconductor layer with a predetermined width and reaching the inside of the normal conductor layer to manufacture a Josephson junction device.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a Josephson junction element and a method for manufacturing the same. More specifically, it relates to improvements in Josephson junctions and methods of forming the same.

[0002]

2. Description of the Related Art Recently, La series, lanthanoid series including Y, B series
Oxide superconductors such as i-based or T1-based oxides are receiving attention. Compared with conventional metal-based and alloy-based superconducting materials, these have the advantage that they can be cooled with liquid nitrogen because they have a higher critical temperature, and are extremely useful materials in practical use.

The conventionally proposed Josephson junction elements are roughly classified into two types. One is a superconductor-
It is an insulator-superconductor junction element (so-called SI-S type junction element), and the other is a superconductor-normal conductor-superconductor junction element (so-called SNS type junction element). SIS
The type junction element has a so-called laminated structure in which an ultrathin insulating film having a film thickness corresponding to the coherence length of the superconductor or less is interposed between two superconductors. The elemental composition ratio, the compositional uniformity, and the film thickness may greatly influence the bonding characteristics and reliability. In particular, the oxide superconductor has a short coherence length of about several Å. Therefore, the SI using the oxide superconductor is used.
The -S-type junction element is difficult to manufacture because it is necessary to make the insulating film uniform in the Å order.

On the other hand, the S-N-S type junction element is an S-N-
The S-type junction is a proximity effect type junction that uses the seepage of the wave function from the superconductor to the normal conductor. Also S-N-S
The bonding characteristics of the junction element greatly depend on the characteristics and forming method of the normal conductor layer, but since the width of the seepage of the wave function in the superconducting state to the normal conductor layer is several hundred Å to several thousand Å, SI-
It can be said that it is easier to manufacture than S-type bonding. The S-N-S type junction element is mainly classified into a laminated type and a planar type. In particular, the planar type is relatively manufactured because it is basically required to form only two layers of a normal conductor layer and a superconductor layer. It can be said that it is easy to perform and has good manufacturing reproducibility, but it requires microfabrication with a width of several hundred Å to several thousand Å at the joint.

[0005]

The above-mentioned conventional planar type S-N-S type junction element has a problem that it is difficult to finely process the junction portion. The present invention has been made to solve the above problems, and an object of the present invention is to provide a Josephson junction element with good performance that enables easy microfabrication of the junction portion with high accuracy, and a method for manufacturing the same. Is.

[0006]

According to the present invention, a normal conductor layer and a superconductor layer are sequentially laminated on a substrate and patterned in a dumbbell shape, and the bridge portion traverses the superconductor layer. There is provided a Josephson junction element in which a groove which penetrates and reaches the inside of the normal conductor layer is formed.

The Josephson junction element of the present invention can be manufactured, for example, as follows. That is, a) a step of sequentially laminating a normal conductor layer and a superconductor layer on a substrate, and b) forming a photoresist layer on this and etching so that the superconductor layer in a predetermined region is exposed, By supplying metal vapor from the direction inclined at a predetermined angle to the photoresist side with respect to the normal to the superconductor layer surface, leaving a region on the superconductor layer extending over a predetermined width from the etching end face of the photoresist layer to other regions. A step of depositing a first metal layer, c) a step of penetrating the superconductor layer with a predetermined width using the first metal layer as a mask, and forming a groove reaching the inside of the normal conductor layer, and d) a photoresist layer. And the first metal layer thereon are removed, a second metal layer is formed in the removed region, and the remaining first metal layer, second metal layer, superconductor layer and normal conductor layer are patterned in a dumbbell shape. Josephson consisting of process It is a method of manufacturing a case element.

In the present invention, a) a normal electric current is provided on the substrate.
A conductor layer and a superconductor layer are laminated in order. The substrate is acid
It is possible to use a compound single crystal, for example, S
rTiO₃(100), SrTiO₃(110), MgO
(100) and the like. The normal conductor layer is, for example,
Nb-doped SrTiO₃, PrBa₂Cu ₃
O_7-X(However, X is 0 to 1), Bi₂Sr₂CaCu₂O₃
And the like can be used. This film thickness is
It is usually 300-5000Å.

The superconductor layer is made of, for example, YBa ₂ Cu ₃ O.
_7-X (where X is _{0~1), (La 1 -X M} X) 2 CuO 4 (M
= Ba, Sr, Ca, X is 0 to 1), LnBa ₂ Cu ₃ O
_7-X (X is 0 to 1), Ln ₅ Ba ₆ Cu ₁₁ O _X (Ln = N
d, Pm, Sm, Eu, Gd, Dy, Ho, Er, T
m, Yb), Bi ₂ Sr ₂ Ca ₂ Cu ₃ O ₁₀ , Bi _1.7 Pb _0
.2 Sb _0.1 Ca _2.0 Sr _2.0 Cu _2.8 O _x (X is 10),
(Bi _0.7 Pb _0.3 ) ₂ Sr ₂ Ca ₂ Cu ₃ O ₁₀ , Tl ₂ Ba ₂
Ca ₂ Cu ₃ O ₁₀ , Ba _1-X K _X BiO ₃ (X is 0 to 1),
A material composed of Nd _2−x Ce _x CuO _4−y (X is 0 to 1 and Y is 0 to 1) can be used. This film thickness is usually 500 to 2000Å.

These laminated layers are formed by, for example, reactive vapor deposition method, sputtering method, laser vapor deposition method, ion cluster beam method, C
It can be performed using the VD method or the like. In the present invention, b) a direction in which a photoresist layer is formed thereon and etched so that a superconductor layer in a predetermined region is exposed, and then a predetermined angle is inclined to the photoresist side with respect to the normal line of the superconductor layer surface. By supplying the metal vapor from the first metal layer, the first metal layer is vapor-deposited on the other region, leaving a region on the superconductor layer extending over a predetermined width from the etching end face of the photoresist layer.

The photoresist layer prevents metal from being deposited on a region on the superconductor layer extending over a predetermined width from the etching end face of the photoresist layer in the step of supplying the metal vapor from the direction inclined to the photoresist side by a predetermined angle. It is to be left, and is etched so that the end face is arranged at the end of the remaining region so that metal is not deposited.

The predetermined angle is usually 5 to 80 degrees, preferably 5 to 20 degrees. The predetermined width can be set to a desired width by appropriately selecting this angle. This angle is usually set by tilting the substrate with respect to the vapor deposition metal supply source in the vapor deposition apparatus. The above predetermined width is
Usually 200 to 50,000Å, preferably 500 to 5,000
It is Å.

The first metal layer is for masking the superconductor layer other than the region where the groove is formed in the step of forming the groove and forming one electrode on the superconductor layer. It is formed by stacking Au, Ag, Al and the like on the superconductor and the photoresist layer by a vapor deposition method or the like. In the present invention, c) the first metal layer is used as a mask to form a groove that penetrates the superconductor layer with a predetermined width and reaches the inside of the normal conductor layer. The predetermined width is usually 200 to 500
00Å preferably 500 to 5000Å.

In the groove, the electric current that has reached the groove through one of the superconductor layers is made to flow along the groove of the normal conductor layer and is made to flow in the other superconductor layer separated by the groove to form a planar type S. -N-
It is for constructing an S Josephson junction. The groove separates the superconducting layer at the above-mentioned predetermined interval and reaches the inside of the normal conducting layer. The depth of the inside of the normal conductor layer of the groove is usually 20 to 3000Å, preferably 50 to 10
It is 00Å. This groove is usually formed by an anisotropic dry etching method, for example, a reactive ion etching apparatus, an ion beam etching apparatus or the like is used.

In the present invention, d) the photoresist layer and the first metal layer thereon are removed, a second metal layer is formed in the removed region, and the remaining first metal layer, second metal layer and superconductor are formed. The layer and the normal conductor layer are patterned into a dumbbell shape to produce a Josephson junction device. The Josephson junction device obtained by the present invention is a planar S-N-S junction, and one superconducting layer and the other superconducting layer can be completely separated from each other. If there is no short-circuit problem of the superconductor and the groove depth at the junction is appropriately formed, good Josephson junction characteristics can be obtained with good reproducibility.

[0016]

The photoresist layer partially blocks the metal vapor supplied from the direction inclined to the photoresist side by a predetermined angle to prevent the metal from being vapor-deposited on the superconductor layer over a predetermined width from the etching end face of the photoresist layer. It is formed, and this region is etched to form a groove forming an S-N-S Josephson junction.

[0017]

Embodiments of the present invention will be described with reference to the drawings.
An explanatory view of the produced Josephson device is shown in FIG. The normal conducting layer 12 is formed on the substrate 11, and the superconducting layer 1 is formed on the normal conducting layer 12.
3, 13 'were formed. Further, metal layers 14 and 14 'were formed thereon as electrodes. Further, a groove 15 having a width 16 of several hundred Å to several thousand Å was formed by dry etching.
The superconducting layers 13 and 13 'are completely separated by the groove 15, and there is no short circuit between the superconducting layers. Therefore, the superconducting current flows from the superconducting layer 13 to the normal conducting layer 12 near the groove 15.
To flow into the superconducting layer 13 '. Groove 15
If the normal conductive layer in the vicinity has a length of several hundred to several thousand Å, an S-N-S type Josephson junction is formed by the proximity effect.

Next, the manufacturing process of the device will be described with reference to FIG. First, as shown in FIG. 2A, SrTi
The single crystal substrate 11 of O ₃ (100) is heated to 650 ° C.,
Nb-doped SrTiO ₃ is formed using the reactive vapor deposition method.
The thin film 12 has a composition ratio of Sr and Ti of 1: 1 and a doping amount of Nb of 0.5 with respect to the weight ratio of SrTiO _3.
The amount of vapor deposition was adjusted to be 100%, and a 1000 Å deposition film was formed. At that time, 10% ozone was applied to the substrate so that the Nb-doped SrTiO ₃ thin film was sufficiently oxidized.
The vapor deposition was performed while irradiating the contained oxygen radicals.
The degree of vacuum near the pump at that time is 8.5 × 10 ^-5 Tor
It was r. Nd = dopedSrTiO ₃ is the N
The carrier concentration can be modulated by the doping amount of b, and it is known to be an n-type semiconductor.

Next, as shown in FIG. 2B, the substrate temperature is
While maintaining the temperature at 650 ° C, the reactive vapor deposition method was used in the same manner.
YBa₂Cu₃O_7-XThe composition ratio of the thin film 13 is Y: B.
a: Cu = 1000: Å deposited film to be 1: 2: 3
It was Nb-doped SrTiO ₃As with thin films, oxidation
In order to accelerate it, the film is exposed to oxygen-ozone radicals during film formation.
Shot After cooling, the substrate is removed from the chamber and
As shown in (c), half of the substrate is covered with the resist 21.
Patterning was performed. The resist at this time
The thin film of was 1 μm.

Next, as shown in FIG. 2D, the substrate 11
Is tilted about 10 degrees in the direction of the resist surface from the direction normal to the substrate and the vapor deposition source (metal vapor supply source).
4'was deposited by 5000Å. In short, the shadow portion of the resist was in a state where Au was not deposited. The degree of vacuum near the pump during vapor deposition was 5 × 10 ⁻⁶ Torr. If the deposit 22 ideally flies to the substrate in a straight line, 10
With the inclination of the substrate of 10 degrees, the uncoated portion was calculated to be about 1700 Å, but the actual groove width 16 was 700 Å due to the inclusion of the deposited material.

Next, as shown in FIG. 2 (e), a groove 15 having a width of 700Å was formed by irradiating the substrate with an Ar ion beam 23 perpendicularly. The depth of the groove 15 is
It was 1200 Å from the surface of the superconducting layer 13. By forming the groove 15, the superconducting layer 13 is
It is completely separated into 3'and there is no possibility of leakage between the superconducting layers. The normal conductive layer 12 has a depth of 200.
Since it is Å, the junction width of the normal conductive layer is 200 Å + 700 Å
+200 Å = 1100 Å, and we were able to obtain a length that can be expected to connect the superconducting layers due to the proximity effect.

Next, as shown in FIG. 2 (f), the resist 21 on the superconducting layer 13 and the Au thin film 14 are peeled off by ultrasonic cleaning with acetone, and as shown in FIG. An Au thin film 14 ′ was vapor-deposited on the layer 13. Finally,
A dumbbell-shaped resist was formed, and etching was performed by irradiation with an argon ion beam to finally obtain a device structure as shown in FIG. The bridge width 17 was 5 μm.

FIG. 3 shows the current-voltage characteristics of the Josephson device manufactured in this example. The obtained IcRn product is m
It was V. In addition, as a result of irradiating the bridge portion with a microwave of 10.8 GHz at T = 77 K, a Shapiro step of about 20 μV was observed in the current-voltage characteristic. This can be considered that a good Josephson junction is formed in the bridge portion. Further, in this example, the bonding width was set to 700 Å, but as a result of vapor deposition of Au by changing the inclination of the substrate, a Shapiro step by microwave irradiation was confirmed from 20 Å to 50000 Å.

[0024]

According to the present invention, the width of the joint portion is 200 mm.
It is possible to provide a Josephson junction device having good performance by which a groove of ˜50000Å can be easily formed with high precision and a method for manufacturing the same.

[Brief description of drawings]

FIG. 1 is an explanatory diagram of a Josephson junction device manufactured in an example of the present invention.

FIG. 2 is likewise an explanatory view of the manufacturing process.

FIG. 3 is a diagram of current-voltage characteristics similarly.

[Explanation of symbols]

 11 Substrate 12 Normal Conduction Layer 13, 13 'Superconducting Layer 14, 14' Metal Layer 15 Groove 16 Groove Width 17 Bridge Width

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Masayoshi Kiba 22-22 Nagaike-cho, Abeno-ku, Osaka-shi, Osaka

Claims (4)

[Claims] 1. A normal conductor layer and a superconductor layer are sequentially laminated on a substrate and patterned in a dumbbell shape, and a bridge portion of the normal conductor layer and the superconductor layer traverses and penetrates the superconductor layer. A Josephson junction device in which a groove reaching the inside is formed. 2. A groove is _0. Josephson device according to claim 1 having a width of 02～5Myuemu. 3. A step of a) laminating a normal conductor layer and a superconductor layer in this order on a substrate, and b) a photoresist layer formed thereon, and etching so that the superconductor layer in a predetermined region is exposed. After that, metal vapor is supplied from a direction inclined at a predetermined angle toward the photoresist with respect to the normal to the surface of the superconductor layer, leaving a region on the superconductor layer extending over a predetermined width from the etching end surface of the photoresist layer. A step of depositing a first metal layer in the region of c), c) a step of penetrating the superconductor layer with a predetermined width using the first metal layer as a mask, and forming a groove reaching the inside of the normal conductor layer, d) Removing the photoresist layer and the first metal layer over it,
A method of manufacturing a Josephson junction device, comprising the step of forming a second metal layer in the removed region and patterning the remaining first metal layer, second metal layer, superconductor layer and normal conductor layer in a dumbbell shape. . 4. The predetermined angle is 5 to 80 degrees.
Manufacturing method.