JP3005434B2 - Superconducting device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention
r-Ti-O substrate and Ba-K formed on this substrate
The present invention relates to a superconducting device having a Bi-O superconducting layer, and more particularly to improvement in conductivity between a substrate and a superconducting device.

[0002]

2. Description of the Related Art Recent advances in superconducting electronics have been remarkable, and various superconducting devices have been proposed. Among such superconducting devices, a superconducting base three-terminal element (transistor) using an oxide superconductor as a base layer has been attracting attention.
There are various proposals for this as well.

For example, a superconducting three-terminal device as shown in FIG. 3 has been proposed. In this three-terminal device, STO (SrTi _1-x Nb _x O ₃ ) doped with Nb as an impurity is used.
A BKBO (Ba _0.6 K _0.4 BiO ₃ ) superconducting layer 12 is formed on a substrate 10.
u layer 14 is formed on the back surface of the STO substrate.
An electrode layer 18 is formed. Then, the STO substrate 10
Is the collector, BKBO superconducting layer 12 is the base, Au layer 1
4 functions as an emitter.

[0004]

The superconducting three-terminal element has a Schottky barrier formed between the STO substrate and the BKBO superconducting layer, as shown in FIG. And
Due to this Schottky barrier, the transmittance of low-energy quasiparticles (carriers) is reduced, and there has been a problem that a sufficient current amplification factor and voltage amplification factor cannot be obtained as a three-terminal device.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and it is an object of the present invention to remove a barrier between layers.
It is an object of the present invention to provide a superconducting device that can increase the transmittance of low energy carriers.

[0006]

Means for Solving the Problems The present invention includes a Sr-Ti-O substrate containing a predetermined impurity, the Sr-Ti-O
A superconducting device having a Ba-K-Bi-O superconducting layer formed on a substrate, wherein the Sr-Ti-O substrate and
During the Ba-K-Bi-O superconducting layer, or Sr-Ti-O
Rannahli, than the content of impurities of the Sr-Ti-O board
An intermediate layer containing a large amount of impurities is formed.

In the present invention, it is preferable that the impurity of the Sr—Ti—O substrate is La . Furthermore, the above
The impurity in the intermediate layer is preferably La.

[0008]

As described above, according to the present invention, Sr-Ti-O
An intermediate layer of STO having an impurity concentration higher than that of the STO substrate is formed between a substrate (hereinafter, referred to as an STO substrate) and a Ba-K-Bi-O superconducting layer (hereinafter, referred to as a BKBO superconducting layer). Therefore, the presence of this intermediate layer makes it possible to set the energy band structure to a smooth one, and prevent the occurrence of a Schottky barrier. Therefore,
The movement of low-energy carriers between the STO substrate and the BKBO superconducting layer is promoted, and the current amplification factor and the voltage amplification factor when a three-terminal element is formed can be increased.

In particular, by setting the impurity of the substrate to La or the impurity of the intermediate layer to La, it is possible to preferably prevent the occurrence of a barrier.

[0010]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a diagram showing a configuration of an embodiment,
STO doped with Nb as an impurity (SrTi _1-x N
BKBO (Ba _0.6 K _0.4 Bi) on a (b _x O ₃ ) substrate 10
O ₃ ) A superconducting layer 12 is formed. Where STO
X which determines the impurity concentration in the substrate 10 is about x = 0.01, and the number of carriers at this time is about 2 × 10 ¹⁹ / cm.
It becomes ³ .

On the BKBO superconducting layer 12, Au is applied.
A layer 14 is formed. Further, an Au electrode layer 16 is formed on the back side of the STO substrate.

An intermediate layer ( Sr _{1 -x} La _x TiO ₃ ) 20 is formed between the STO substrate 10 and the BKBO superconducting layer 12. This intermediate layer 20 is
It is an STO like that described above, but La is diffused as an impurity. The intermediate layer 20 has a thickness of 10 to 20 n.
m. Then, x in the intermediate layer 20 is about 0.04 to 0.2 (particularly preferably about 0.05 to 0.1), and the number of carriers is 1 × 10 ^{22 to} 5 × 10 2.
It is set to ²² / cm ³ .

With the superconducting device having such a structure, the STO substrate 10 serves as a collector and a BKBO superconducting layer 12.
Function as a base, and the Au layer 14 functions as an emitter.

The energy band of each layer when the intermediate layer 20 is present is as shown in FIG. That is, due to the presence of the intermediate layer 20, the change in the energy level at the interface between the intermediate layer 20 and the STO substrate 10 and the BKBO superconducting layer 12 on both sides thereof becomes smooth, and the interface between the BKBO superconducting layer 12 and the STO substrate The intervening Schottky barrier is removed. Therefore,
The movement of charges at the interface becomes smooth, and the movement of low-energy carriers becomes possible. Therefore, it is possible to increase the current / voltage amplification factor in a three-terminal element or the like using this superconducting device.

Here, the diffusion of the impurity (La) in the intermediate layer 20 may be uniform in the thickness direction of the intermediate layer 20, but it is also preferable that the impurity amount is inclined. That is, La is diffused on the BKBO superconducting layer 12 side so that the carrier concentration becomes 1 × 10 ^{22 to} 5 × 10 ²² / cm ³ , but the impurity concentration on the STO substrate 10 side is made relatively low, and The barrier at the interface can be removed by reducing the difference in diffusion potential at the interface between the STO substrate 20 and the STO substrate 10. The inclination of the impurity concentration may be performed as a whole in the thickness direction.
A concentration of about 10 nm on the O superconducting thin film 12 side is set to a constant concentration.
Only about 10 nm on the TO substrate 10 side may be inclined.

Next, the fabrication of the superconducting device will be described. First, Nb is x = 0.01 as an impurity.
An STO substrate 10 to which a degree of addition is prepared is prepared. Then, Au is deposited on the back surface of the STO substrate 10 by electron beam evaporation.
The electrode layer 16 is formed. Next, the intermediate layer 20 is formed on the STO substrate 10. This intermediate layer 20 has the same S
After being made of TO and having a dopant on the surface, ions of a predetermined concentration are diffused into the layer by thermal diffusion and annealed. For example, this is performed as follows. First, the sputtering chamber is evacuated to 1 × 10 ⁻⁵ Pa, and then the substrate temperature is set to 570 to 620 ° C. And the gas flow rate is O
₂ : Ar is set to 1: 1 and sputtering is performed while flowing a gas of 80 Pa in total. The STO-La target is Sr
_This is a powder target obtained by solidifying _1-x La _x TiO ₃ powder by pressing, and has a film formation rate of 0.01 nm / sec.
After the sputtering, the O ₂ gas was reduced to about 1 atm for reconstitution of the STO substrate surface and diffusion of La.
Anneal at about 1100 ° C. for several minutes, cool down to 700 ° C. over about 10 minutes, and then cool down over about several hours. The formation of the STO layer and the formation of the dopant on the surface of the STO substrate 10 are not limited to sputtering, but may be deposition using a conventional method such as MBE (molecular beam epitaxy), laser deposition, or CVD (chemical vapor deposition). Phase growth) and the like are used. Also,
The impurity addition to the intermediate layer 20 may be performed by ion implantation in addition to the above-described method using thermal diffusion. In this case, a predetermined impurity concentration can be formed at an arbitrary depth position and an arbitrary substrate position by controlling the energy of the ions to be implanted, the implantation time, the implantation position, and performing heat treatment as necessary.

Then, BKBO is placed on the obtained intermediate layer 20.
The superconducting layer 12 is formed to a thickness of 5 to 200 nm by RF magnetron sputtering. The BKBO superconducting layer 12 is formed, for example, as follows. First,
After evacuating the sputtering chamber to 1 × 10 ⁻⁵ Pa, the substrate temperature is set at 300 to 400 ° C. And
The gas flow rate was set to O ₂ : Ar = 1: 1, and a total of 80 Pa
Is sputtered while flowing the above gas. The BKBO target is a powder target obtained by solidifying BKBO powder by pressing, and has a film formation rate of 0.01 nm / sec. This BKB
For the O film formation, MBE (molecular beam epitaxy), laser evaporation, CVD, or the like is used. After the film formation, as an annealing treatment of the film, O ₂ gas is injected into the chamber to 4 to 5 atm and cooled from 400 ° C. for several hours.

Further, an Au layer 14 is formed on the BKBO superconducting layer 12 by electron beam evaporation. This formation is 9
A pellet of Au having a purity of 9.9% or more is prepared, the degree of vacuum is set to 1 × 10 ⁻⁴ Pa, and the substrate temperature is set to room temperature to 400 ° C.
C., a film forming speed of 0.3 to 1 nm / sec, an emission current of 100 mA, and a beam acceleration voltage of 3 kV, and patterning into a predetermined shape.

The Au electrode layer 16 is formed in the same manner. As the impurities of the STO substrate 10 and the intermediate layer 20, the above-mentioned Nb and La are preferable.
Y, La, Pr, Nd, Pm, Sm, Eu, Gd, T
+3 among b, Dy, Ho, Er, Tm, Yb and Lu
Valuable ones can be selected.

[0020]

As described above, according to the present invention,
The impurity concentration is ST between the STO substrate and the BKBO superconducting layer.
An intermediate layer of STO higher than the O substrate is formed. Therefore, the presence of the intermediate layer can set the energy band structure to a predetermined one, and can prevent the occurrence of a Schottky barrier. Therefore, the movement of low-energy carriers between the STO substrate and the BKBO superconducting layer is promoted, and the current amplification factor and the voltage amplification factor when a three-terminal element is formed can be increased.

In particular, by setting the impurity of the substrate to La or the impurity of the intermediate layer to La, it is possible to preferably prevent the occurrence of the barrier.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating an overall configuration of an embodiment.

FIG. 2 is a diagram showing an energy band structure of an example.

FIG. 3 is a diagram showing an entire configuration of a conventional example.

FIG. 4 is a diagram showing an energy band structure of a conventional example.

[Explanation of symbols]

 Reference Signs List 10 STO substrate 12 BKBO superconducting layer 14 Au layer 16 Au electrode layer 20 Intermediate layer

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-2-91981 (JP, A) JP-A-6-310768 (JP, A) JP-A-4-328882 (JP, A) (58) Field (Int.Cl. ⁷ , DB name) H01L 39/22 H01L 39/24 H01L 39/00 H01L 39/02

Claims (3)

(57) [Claims] 1. Sr—Ti—O containing predetermined impurities
Substrate and a Ba- layer formed on the Sr-Ti-O substrate.
A superconducting device having a K-Bi-O superconducting layer, comprising Sr-Ti-O between the Sr-Ti-O substrate and the Ba-K-Bi-O superconducting layer , wherein the Sr-Ti-O
A superconducting device, wherein an intermediate layer containing impurities larger than the impurity content of the substrate is formed. 2. The superconducting device according to claim 1, wherein the impurity in the Sr—Ti—O substrate is La . 3. A superconducting device according to claim 1, wherein
Wherein the impurity in the intermediate layer is La.
Conduction device.