JP3281738B2 - Vortex flow transistor and method of manufacturing the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a vortex flow transistor, which is a superconducting computer, a superconducting digital circuit, or a superconducting circuit element such as a superconducting quantum device, and a method of manufacturing the same.

[0002]

2. Description of the Related Art A vortex flow transistor or a flux quantum flow device is a type II device which is placed in a lower critical magnetic field.
The quantized magnetic flux (flux quantum or vortex) present in the seed superconductor or superconducting thin film is accelerated by the bias current and moves in the channel. As a result, the moving vortex This is an amplification type superconducting three-terminal element that utilizes the fact that a voltage proportional to speed is generated. Since the output voltage is proportional to the number of vortices, that is, the externally applied magnetic field, the output voltage is proportional to the current of the control line arranged near the channel. The vortex flow transistor is a current input voltage output type transistor.

Conventionally, there has been an element called a Josephson vortex flow transistor. This element utilizes the running of a vortex present in a Josephson junction line. This is distinguished from the former vortex as Josephson vortex, and the vortex used in the present invention is referred to as abrikosov vortex.
Further, the above-mentioned element has a small output of only several hundred μV, and has a problem in impedance matching with a semiconductor circuit or the like.

[0004] A vortex flow transistor utilizing an abrikosov vortex in a high-temperature superconductor has the advantage that the output voltage can be as large as several tens of mV, but the proportional region of the output voltage to the control current is narrow, and the rise control is difficult. There were drawbacks such as a large current. Furthermore, since the channel was formed by a method of chemically or physically removing a part of the upper part of the superconducting thin film, the thickness of the channel portion fluctuated from element to element, and the reproducibility of characteristics was poor. There were drawbacks.

[0005]

In order to improve the characteristics of the vortex flow transistor, the relationship between the control current and the output voltage requires a wide linear region and a small control current results in a large output voltage ( High gain)
It is required that the control current when the output voltage rises be as small as possible. For that purpose, a channel format with good vortex flow characteristics is essential. In order to improve the vortex flow characteristics, it is necessary that the vortex viscosity coefficient η is small and that the vortex can easily enter the channel portion even with a weak magnetic field.
The upper critical magnetic field is H _C2 , the flux quantum is Φ ₀ , and the normal conduction resistance is ρ _n
Then, since approximately η = Φ ₀ H _C2 / ρ _n c ² , H
May be _C2 is small [rho _n large, since the [rho _n and H _C2 is the substance-specific value, the structure will be approximately determined by the superconductor is used properties if the same. However, in the case of a very thin thin film, as the film thickness decreases, H _C2 decreases and ρ _n increases equivalently. Therefore, in order to form a channel having good vortex flow characteristics, the thickness of the channel portion may be extremely small. If the channel portion is formed of a superconductor thin film having a very small thickness and a small H _C2 and a large ρ _n , it is expected that the flow characteristics of the channel will be further improved. You.

[0006] The channel of the conventional vortex flow transistor forms continuous holes in the superconducting thin film,
Alternatively, grooves are formed in the thin film by physical methods such as chemical or ion milling methods, and the superconducting characteristics of the channel part are deteriorated, the channel thickness differs for each element, or the characteristics are different There was a disadvantage.

The present invention provides a method for manufacturing a vortex transistor and a channel with good controllability, comprising a channel having excellent vortex flow characteristics as described above, and thereby improving the characteristics of the vortex flow transistor. With the goal.

[0008]

The above object is achieved by the present invention.
As described, the thickness of the superconducting thin film
Vortex (magnetic flux quantum)
Set the running channel and the number of vortexes
A superconducting control line to be controlled
In the case of a lutex flow transistor, the above channel
Other than the superconductor part that constitutes the channel
It consists of two layers with other superconductors
Configuring a vortex flow transistor, and
The vortex runs as described in claim 3.
Superconducting thin film with a flowing channel and running vortex
Volts consisting of superconducting control lines that control the number of
Flow transistors other than the above channels
Remove the first superconducting thin film by patterning, leaving a part
In the first step and on the remaining pattern and substrate,
Depositing a second superconducting thin film of the same type or a different type
The second step, and leaving the superconductor portion including the channel.
A third step of removing the superconducting thin film deposited in the second step.
Vortex float characterized by comprising a process
This is achieved by configuring a method for manufacturing a transistor .

That is, the channel portion of the vortex flow transistor is made thinner than other portions,
And, instead of a method such as chemical etching or ion milling, or convergent ion beam milling, which has been conventionally used as a channel forming method, a superconducting thin film having the same or different vortex flow characteristics in the channel portion is used. A vortex flow channel is newly formed in another process to form a vortex flow channel, and a vortex flow transistor having excellent characteristics is manufactured.

[0010]

[Function] In order to improve the characteristics of the vortex transistor, a superconductor having a small H _{C2 and a} large ρ _n may be used as described above. However, if the H _C2 is too small, the vortex interval increases, and the traveling vortex increases. Cannot be obtained because of the decrease in the number of. On the other hand, in a high-temperature superconductor, H _C2 is not small, but ρ _n is large, and η is small, so that it is excellent as a superconductor for forming a channel. In particular, Bi ₂ Sr ₂ CaCu ₂ O ₈ or (Bi _1-x P
b _x ) ₂ Sr ₂ Ca ₂ Cu ₃ O ₁₀ (x <0.35) (hereinafter B
Since the i-type superconductor) has a large two-dimensional property, the flux lattice is melted in a wide temperature range and the effect of collective pinning is lost, so that the vortex is easily run and the superconductor is suitable for a channel.

The superconductor excellent for forming the channel can be used in the same manner as the superconductor even when Bi, Sr, and Ca fluctuate by about 10%, respectively.

On the other hand, when the thickness of the channel is reduced, the demagnetizing field coefficient increases, and the apparent lower critical magnetic field H _C1 decreases. Therefore, with a weak externally applied magnetic field, the vortex can penetrate into the channel portion with a small control current. High-temperature superconductors having a layered structure and particularly Bi-based superconductors having large anisotropy have the same properties even when H _C1 is small, so that the same effects can be expected without making them extremely thin. . Therefore, there is an advantage that processing is easy.

When the thickness of the channel portion is reduced, the method of shaving the upper portion of the thin film is difficult to control the shaving depth, and the remaining portion is damaged and the superconductivity is deteriorated. In addition, if the thickness of the thin film varies, the thickness of the channel varies, and there are many disadvantages such that the reproducibility of the channel characteristics cannot be obtained. On the other hand, the superconducting layer having the thickness necessary for the thickness of the channel is removed, except for the portion other than the channel except for the channel (2 in FIG. 1). After depositing the thin film (3 in FIG. 1), if the other portions are removed except for the entire device including the channel (6 in FIG. 1), the channel portion is not exposed to damages caused by processes such as etching. By controlling the film thickness when depositing the second thin film, a constant thickness can always be obtained. Also, the second
It is also possible to use a different type of superconducting film from the first superconducting film. In this way, a channel having excellent vortex flow characteristics can be formed, and the characteristics of the vortex flow transistor can be improved.

When depositing the second superconducting thin film, the first superconducting thin film is exposed to a vacuum at a high temperature, so that the surface properties are deteriorated to some extent due to oxygen deficiency.
Therefore, there may be a case where the electrical contact with the second superconductor is insufficient. In such a case, by performing a heat treatment in an oxygen atmosphere after depositing the second thin film, the missing oxygen is compensated, the characteristics of the interface are restored, and good electrical contact is obtained. The heat treatment after the deposition of the second thin film is performed in an oxygen atmosphere at 500 ° C. or higher.
Even if heat treatment is performed at a temperature lower than 500 ° C., no remarkable effect can be obtained on the recovery of oxygen deficiency, and therefore,
The interface resistance cannot be reduced. By the method of the present invention described above, the problems of the vortex flow transistor which have been a problem in the related art can be solved.

[0015]

Next, an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a perspective view showing the concept of an embodiment of a vortex flow transistor according to the present invention.

First Embodiment Bi ₂ Sr ₂ CaCu ₂ O ₈ (hereinafter Bi 22) is formed on a (100) plane substrate (hereinafter referred to as an STO substrate) 1 of SrTiO _{3 by} a high frequency sputtering method at a substrate temperature of 650 ° C.
12) was deposited to a thickness of 200 nm. Then, using photolithography technology and ion milling technology,
The superconducting wiring pattern shown in No. 2 was obtained. The superconducting wiring pattern does not include a channel portion. The length of the channel, that is, the width of the superconducting wiring was 50 μm, and the width of the channel was 5 μm. Next, Bi2212 having a thickness of 50 n was formed on the patterned superconducting wiring obtained in this manner under the same conditions as when Bi2212 of the first layer was grown.
m. Thereafter, the second layer was processed into a pattern having the same channel portion as the pattern in which the first layer was formed, to obtain a vortex flow transistor as shown in FIG.

In the vortex flow transistor obtained as described above, the output voltage rises with a small control current, and the linear region is significantly larger than that of the conventional vortex flow transistor due to the relationship between the bias current and the control current. Expanded.

In FIG. 1, after the second superconducting thin film 3 is grown, it is subjected to a heat treatment at 600 ° C. for 8 hours in oxygen, and then the vortex flow transistor obtained through the same steps as the above steps has a The magnitude of the bias current that is output by the control current is approximately doubled. This is because the interface between the first layer and the second layer is improved and the electrical contact is improved, which is advantageous when the vortex flow transistor is miniaturized and integrated.

Note that Bi ₂ Sr ₂ C is used instead of Bi 2212.
aCu ₂ O ₈ and (Bi _0.8 Pb _0.2 ) ₂ Sr ₂ Ca ₂ Cu ₃
Same effect when using O ₁₀ was obtained.

Second Embodiment A high-frequency sputtering method is applied to an STO substrate at a substrate temperature of 700 ° C. to obtain YBa ₂ Cu ₃ O ₇ (hereinafter referred to as YBCO).
Was grown to a thickness of 200 nm. Thereafter, a patterned superconducting wiring 2 was obtained in the same manner as in the first embodiment.
Next, Bi2212 was grown on the superconducting wiring 2 at a substrate temperature of 650 ° C. to a thickness of 50 nm. Next, a heat treatment was performed at 600 ° C. in oxygen for 8 hours, and a vortex flow transistor as shown in FIG. 1 was obtained through the same steps as in the first embodiment.

In the vortex flow transistor obtained as described above, as in the first embodiment, the output voltage rises with a small control current, and the linear region is the conventional region due to the relationship between the bias current and the output voltage with respect to the control current. It is significantly larger than the vortex flow transistor.

[0022]

As described above, according to the vortex flow transistor and the method of manufacturing the same according to the present invention, a portion of the superconducting thin film where the thickness of the thin film is thinner than other portions is set as a channel through which vortex (magnetic flux quantum) travels. And arranging a superconducting control line for controlling the number of vortices near the channel, and manufacturing the vortex flow transistor by removing a first superconducting thin film except for a portion other than the channel. A second step of depositing a second superconducting thin film of the same type or a different type on the remaining pattern and substrate, and a second step excluding a portion including a channel. By including the third step of removing the superconducting thin film, the channel can be manufactured with good controllability, and the linear region is significantly expanded in the relationship between the control current and the output voltage. Can, raises the output voltage with a small control current, it is possible to obtain a vortex flow transistor having a large output voltage is obtained.

[Brief description of the drawings]

FIG. 1 is a perspective view showing the concept of an embodiment of a vortex flow transistor according to the present invention.

[Explanation of symbols]

 2 First superconducting thin film 3 Second superconducting thin film 5 Superconducting control line 6 Channel

──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor ▲ Tsuru ▼ Koji 1-6-1, Uchisaiwaicho, Chiyoda-ku, Tokyo Nippon Telegraph and Telephone Corporation (72) Shugo Kubo 1-1-1, Uchisaiwaicho, Chiyoda-ku, Tokyo No. 6 Inside Nippon Telegraph and Telephone Corporation (72) Keiichi Tanabe Inventor 1-6-6 Uchisaiwaicho, Chiyoda-ku, Tokyo Nippon Telegraph and Telephone Corporation (56) References JP-A-5-291635 (JP, A) JP-A-62-117194 (JP, A) JP-A-64-21974 (JP, A) JP-A-64-31478 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H01L 39 / 22-39/24 H01L 39/00

Claims (4)

(57) [Claims] 1. A superconducting thin film in which the thickness of the thin film is smaller than that of other portions is used as a channel through which vortex (magnetic flux quantum) travels, and a superconducting control line for controlling the number of vortices is provided. Vortex flow transistors located near the channel
The superconductor part of the
A vortex flow transistor comprising two layers of a superconductor other than the above . 2. The vortex flow transistor according to claim 1, wherein the superconductor forming the channel is B
i ₂ Sr ₂ CaCu ₂ O ₈ or _(Bi 1-x _Pb x)
A vortex flow transistor comprising ₂ Sr ₂ Ca ₂ Cu ₃ O ₁₀ (x <0.35) . 3. A vortex flow transistor comprising a superconducting thin film having a channel through which a vortex travels and a superconducting control line for controlling the number of vortices traveling, wherein a first superconducting film is formed except for a portion other than the channel. A first step of patterning and removing the conductive thin film, a second step of depositing a second superconducting thin film of the same type or a different type on the remaining pattern and the substrate, A third step of removing the superconducting thin film deposited in the second step while leaving a conductor portion, the method comprising the steps of: 4. A method for manufacturing a vortex flow transistor according to claim 3 , wherein said second superconducting thin film is deposited in said second step, and then said second superconducting thin film is deposited in an oxidizing atmosphere.
A method for manufacturing a vortex flow transistor, wherein a heat treatment is performed at a temperature of not less than ° C.