JPH05211351A - Josephson element and manufacture thereof - Google Patents

Abstract

PURPOSE:To obtain a barrier layer which has a thickness of the order of nm and is high is adhesion strength and small is number of pinholes by a method wherein a chemical adsorbing film is used as the barrier layer which isolates an upper electrode from a lower electrode. CONSTITUTION:A lower electrode 2 of a superconductor is provided on a substrate 1, hydrophilic groups are formed thereon, chlorosilane adsorbent gas which contains straight carbon chain provided with chlorine-silicon chemical bond (-SiClX3-n group, n=2 or 3, X is functional group) at its one end is made to react thereon to enable chemical adsorbing film precursor to be adsorbed, and then the absorbed chemical adsorbing film precursor is formed into an adsorbing film 3 (barrier layer) of -Si(O-)3 through the reaction of hydrolysis, and dehydration condensation. It is preferable that the chemical adsorption process is carried out at least twice or more. An upper electrode of superconductor is formed on the surface of the barrier layer, and thus a Josephson element 5 can be obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a Josephson device to which superconducting technology is applied and a manufacturing method thereof.

[0002]

2. Description of the Related Art When forming a Josephson element, conventionally, when niobium (Nb) was used for a superconducting electrode, alumina (Al ₂ O ₃ ) was used for a barrier layer and niobium nitride (NbN) was used for a superconducting electrode. When using, magnesium oxide (MgO) was used as the barrier layer material. The barrier layer made of oxide material is formed by sputtering method or reactive vapor deposition method, but it is uniform when an extremely thin thin film with a thickness of several nanometers, which is necessary for the construction of Josephson devices, is formed. It is difficult to form a large barrier layer, there is a large leak current due to pinholes, etc., or there is a problem that the yield of the superconducting critical current is large and the yield is poor.
At present, a barrier layer thickness of around 10 nm is used.
Recently, in the Nb-based or NbN-based Josephson junction device having a size of several μm, the variation in the superconducting critical current value can be suppressed to 10% or less by the improvement of the process.

When a Y-based oxide superconductor, a Bi-based oxide superconductor, or a Tl-based oxide superconductor is used as a superconducting electrode, MgO or yttrium oxide (Y ₂₎ as a barrier layer material is used. Oxide materials such as O ₃ ) have been tried, but good tunnel junction type Josephson characteristics have not been obtained yet.

Further, as an example of using an organic material for the barrier layer material, lead bismuth (PbBi) is used for the superconducting electrode, and LB (Langmuir / polyamide acid long chain alkylamine salt (PAAD) LB (Langmuir. (Blodget)
Using a film (Shunichi Shido et al., "Evaluation of LB film by Josephson junction element", IEICE technical report, Organic Electronics, OME88-3 (1988)),
Alternatively, PbBi and Nb are used for the superconducting electrode, and a polyimide LB film is used for the barrier layer (Tetsu Kubota et al., "Electrical characteristics of Josephson junction device using polyimide LB film", IEICE technical report. "Organic electronics" OME90-7 (1990)) has been reported.
However, all of them show weak coupling type Josephson junction characteristics due to the presence of pinholes, and tunnel junction type Josephson characteristics have not been obtained.

[0005]

As described above, the barrier layer made of an oxide-based material is uniform when an extremely thin thin film having a thickness of several nanometers necessary for constructing a Josephson device is formed. It is difficult to form a large barrier layer, there is a large leak current due to pinholes, etc., or there is a problem that the yield of the superconducting critical current is large and the yield is poor. A barrier layer thickness of around 10 nm is used as an allowable value. However, in order to miniaturize the logic circuit using the Josephson element, it is necessary to miniaturize the cell size. For that purpose, the critical current density of the element must be increased and the variation between the elements must be suppressed. I won't.
This means that the thickness of the barrier layer is further reduced, and it is extremely difficult because the conventional combination of materials and the process technology are almost at their limits.

Further, in the barrier layer using the LB film, it is necessary to immerse the substrate in water at the time of forming the LB film, and at this time, the surface of the superconducting electrode is deteriorated or the electrode is peeled off. Further, since the LB film itself is merely physically adsorbed to the lower electrode, the adhesion strength is weak and there is a problem that it easily peels off due to infiltration of water or heat stress. Further, since many pinholes are present in the LB film, tunnel junction type characteristics have not been obtained. It is considered that this is because a large number of pinholes are generated in the domain boundary and the like due to the domains generated during the compression process of the LB film molecules spread on the water surface being fixed in the LB film. Further, there is a problem that the characteristics of the Josephson device are deteriorated due to contamination being mixed in because the substrate is immersed in water.

In order to solve the above-mentioned problems of the prior art, the present invention forms a barrier layer having an ultra-thin nanometer level, which has high adhesion strength and few pinholes. High current density and uniform characteristics,
Moreover, it is an object of the present invention to propose a Josephson device having high reproducibility and a manufacturing method thereof.

[0008]

In order to achieve the above object, a Josephson element of the present invention is a Josephson element including an upper electrode and a lower electrode made of a superconductor, and a barrier layer separating them. The barrier layer is a chemisorption film formed of a linear carbon chain containing a water-repellent group and silicon, and the chemisorption film is formed on at least one surface of the upper electrode or the lower electrode facing each other. It is characterized by being fixed by a covalent bond.

In the above structure, the covalent bond is preferably a siloxane bond. Further, in the above structure, the chemisorption film is preferably covalently bonded to the surface via at least the siloxane-based inner layer film.

Further, in the above constitution, the water-repellent group is preferably a fluorine-containing hydrocarbon group. Next, a method for manufacturing a Josephson device of the present invention is a method for manufacturing a Josephson device including an upper electrode made of a superconductor, a lower electrode, and a barrier layer separating the two. After formation, after introducing a reactive gas to form a hydrophilic group on the surface of the lower electrode, or after forming a siloxane-based chemisorption inner layer film to form a hydrophilic group by the reactive gas,
Chlorsilane-based adsorption that removes the reactive gas and includes a linear carbon chain having a plurality of chlorine-silicon chemical bonds (-SiCl _n X _3-n group, n = 2 or 3, X is a functional group) at one end. After introducing the agent gas into the lower electrode surface to cause an adsorption reaction to form a chemisorption precursor film, the unreacted chlorosilane-based adsorbent gas is removed, and then a reactive gas is introduced to introduce the chemisorption precursor film. It is characterized in that it reacts with the unreacted chlorine-silicon chemical bond of the above to form a silanol group to form a chemisorption film.

In the above structure, the step of forming the chemisorption film is preferably performed at least twice.
In the above structure, it is preferable to use water vapor as the reactive gas.

Further, in the above structure, hydrogen and oxygen are used as the reactive gas, and at the same time when the reactive gas is introduced, the surface of the substrate is irradiated with ultraviolet rays to form a hydrophilic group on the surface of the lower electrode, or chemisorption is performed. It is preferred to react with unreacted chlorine-silicon chemical bonds of the precursor film to form silanol groups.

In the above structure, the chlorosilane-based adsorbent is CF _3- (CF ₂ ) _p- (R) _m --SiCl.
_n X _3-n (p is 0 or an integer, m is 0 or 1, R is a methylene group having a carbon number of 1 or more, a vinylene group-containing methylene group having a carbon number of 1 or more, and a silicon-containing atom having a carbon number of 1 or more. It is preferable that either a group or a methylene group having 1 or more carbon atoms of an oxygen-containing atom, X is a hydrogen atom, a lower alkyl group or a lower alkoxy group, and n is 2 or 3).

[0014]

According to the structure of the present invention, the barrier layer is a chemical adsorption film formed of a linear carbon chain containing a water repellent group and silicon, and at least one of the upper electrode and the lower electrode facing each other. Since the chemisorption film is fixed to the surface by covalent bond, it is possible to form an extremely thin barrier layer of nanometer level, which has high adhesion strength and few pinholes. As a result, a Josephson device with high critical current density, uniform characteristics, and high reproducibility can be realized. That is, the thickness of the barrier layer becomes a constant thickness defined by the length of the chemisorption monomolecule, a uniform tunnel junction can be realized, and the variation in the critical current density between the elements is reduced. The thickness of the barrier layer can also be easily changed by selecting the length of the chemisorption molecule. Furthermore,
The chemical adsorption film containing a linear carbon chain contains a water-repellent group to prevent water from entering, and the fluorine-containing hydrocarbon group is used as the water-repellent group to reduce the leak current and improve the dielectric strength. Therefore, the applied voltage can be increased even with a thin barrier layer. Therefore, the thickness of the barrier layer can be reduced to several nanometers, the critical current density of the Josephson element can be increased, and the variation between the elements can be reduced. Therefore, the cell of the logic circuit using the Josephson element can be reduced. The size can be reduced and the size can be reduced.

Further, since the chemisorption film is fixed to at least one of the superconducting electrodes by a chemical bond, the film has high mechanical strength, and the film is formed by the infiltration of water or heat stress as seen in the LB film. Peeling is unlikely to occur.

Next, according to the method of manufacturing the Josephson device of the present invention, after forming the lower electrode on the substrate, introducing a reactive gas to form a hydrophilic group on the surface of the lower electrode, or a siloxane-based material. After forming a chemisorption inner layer film and forming a hydrophilic group with a reactive gas, the reactive gas is removed,
Chlorine-silicon chemical bond (-SiCl _n X _3-n group, n
= 2 or 3, X is a functional group) and a chlorosilane-based adsorbent gas containing a linear carbon chain having a functional group) is introduced onto the surface of the lower electrode to cause an adsorption reaction to form a chemisorption precursor film and then unreacted chlorosilane. Of the unreacted chlorine of the chemisorption precursor film by removing the system adsorbent gas and then introducing the reactive gas.
Since it reacts with silicon chemical bonds to form silanol groups to form a chemisorption film, the chemisorption film can be efficiently formed. Also, by completely removing the chlorosilane-based adsorbent gas and then introducing the reactive gas, it is possible to remove excess physically adsorbed adsorbent molecules and leave only the chemisorption film. Can react with the unreacted chlorine-silicon chemical bonds of to form silanol groups. By this step, the number of hydroxyl groups of silanol groups that are chemisorption sites is increased, and by further performing this adsorption step at least once, the adsorption density is increased because the chlorosilane-based adsorbent is adsorbed by the hydroxyl groups of silanol groups. .. In addition, since the chlorosilane-based adsorbent has multiple chlorine-silicon chemical bonds only at one end, there is no hydrophilic group (hydroxyl group) that is an adsorption site at the end opposite to the substrate side of the adsorbed molecules that have already been adsorbed. No, the thickness of the molecular adsorption film does not change in this part. Moreover, since the silanol group is present at the end of the chemisorption film on the substrate side, the height of the newly adsorbed single molecule in two or more single molecule adsorption steps does not differ much from that before, so that it is almost uniform. A thick chemical adsorption film can be formed. Therefore, with this method, the pinhole density can be reduced and the leak current can be gradually reduced.

In addition, after forming the lower electrode on the substrate, a chemisorption film is formed in the vapor phase, and then the upper electrode is formed, whereby a Josephson junction is formed in the same vacuum container. Therefore, it is possible to avoid contamination as much as possible, and it is possible to manufacture a Josephson device having stable and favorable characteristics with a high yield. Furthermore, since the chemisorption film is formed in the gas phase, there is also an effect that problems such as deterioration of the surface of the superconducting electrode and film peeling do not occur.

[0018]

[Example] Conventionally, a substrate is contacted with a non-aqueous organic solvent in which a chemical adsorbent is dissolved to cause a chemical reaction in the non-aqueous organic solvent to form a monomolecular film. It is called a reaction. The monomolecular film thus obtained is called a chemisorption monomolecular film. Since the chemisorption monomolecular film is connected to the surface of the substrate through a strong chemical bond, the chemisorption monomolecular film generally has such an adhesive strength that it does not peel unless the surface of the substrate is scraped off. However, as described above, in such a chemisorption reaction in the liquid phase, the amount of contamination contained in the solvent or mixed in the solvent during the manufacturing process causes the monolayer to be separated from the Josephson film. This is a problem when used for a Son element.
Contamination is not preferable because it may increase the leak current, deteriorate the dielectric strength, or cause the Josephson device characteristics such as the superconducting critical current value to vary. In the present invention, in order to solve such a problem in a chemical adsorption reaction in a liquid phase, a method of performing an adsorption reaction in a gas phase is used to form a chemical adsorption film to form a Josephson device. To manufacture. An example will be described below.

FIG. 1 is a sectional view of a Josephson device according to an embodiment of the present invention. A superconducting lower electrode 2 is formed on a substrate 1, a superconducting upper electrode 4 is formed on the substrate 1 with a barrier layer 3 interposed therebetween, and the superconducting upper electrode 4 is cut into a desired shape to form a Josephson device 5. The lower electrode 2 and the upper electrode 4 form a tunnel junction with the insulating barrier layer 3 interposed therebetween. Barrier layer 3
Is a linear carbon chain containing a water repellent group such as fluorine and silicon for chemically bonding, and is chemically bonded to the lower electrode 2 and / or the upper electrode 4 by, for example, a siloxane bond. It is a molecular film. Further, this chemical bond may be a chemical bond via a siloxane monolayer. The barrier layer 3 chemically adsorbs the chemical adsorbent on the lower electrode to form an adsorption film. The chemical adsorption film that is the material of the barrier layer of the present invention may be a monolayer film, a polymer film having a uniform film thickness, or a monomolecular cumulative film. Chemical bonds (covalent bonds) are required even in the cumulative layers.

There are various methods for chemisorption.
As an example, as a chemical adsorbent, chlorosilyl (-Si
Cl_nX_3-n) Group or alkoxysilane (-Si (O
A)_nX_3-n) Group and a hydrocarbon group or
When using a silane-based adsorbent containing elementally substituted carbon
I will explain about this. However, n in the formula is an integer of 1 to 3,
X represents hydrogen, a lower alkyl group or a lower alkoxy group
However, A represents a lower alkyl group. The above silane-based adsorbent
The chlorosilane-based adsorbent has a chemisorption reaction at room temperature.
It is preferable because it can be performed and a chemisorption monomolecular film can be reliably formed.
Yes. Among the chlorosilane-based adsorbents, trichlor-silicon chemistry
If it is a bond (that is, n in the formula is 3), there will be a
It is preferable because it is via a roxane bond. It is also used in the present invention.
Silane-based adsorbents that can be used improve the density of adsorbed molecules
Is preferably linear. Specifically CH₃-(R)_m−
SiCl_nX_3-n, CF₃-(CF₂)_p-(R)_m−
SiCl_nX_3-nThe chlorosilane-based adsorbent represented by
preferable. However, in the formula, p is 0 or an integer, m is 0 or
1, R is methylene group having 1 or more carbon atoms, carbon containing vinylene group
Methylene group with a prime number of 1 or more, silicon atom containing carbon atoms of 1 or more
Methylene group having 1 or more carbon atoms in the above methylene group or oxygen-containing atom
Any of the len groups, X is a hydrogen atom, a lower alkyl group or
Lower alkoxy group, n is an integer of 1 to 3. More concrete
For example, CH ₃(CH₂)₉SiCl₃, CH
₃(CH₂)₁₅SiCl₃, CH₃CH₂O (CH₂)
₁₅SiCl₃, CH₃(CH₂)₂Si (CH₃)
₂(CH₂)₁₅SiCl₃, CF₃(CF₂)₇(CH
₂)₂SiCl₃, CF₃CH₂O (CH₂)₁₅SiC
l₃, CF₃(CH₂)₂Si (CH₃)₂(CH₂)
₁₅SiCl₃, F (CF₂)_Four(CH₂)₂Si (CH
₃)₂(CH₂)₉SiCl₃, CF ₃COO (C
H₂)₁₅SiCl₃, CF₃(CF₂)_Five(CH₂)₂
SiCl₃Etc. Further, the R group in the above formula is vinyl
When it contains a len group, it is exposed to catalyst, light or high energy rays.
Bonding between molecules by polymerizing unsaturated bond
Occurs, and a stronger monomolecular film is formed, which is preferable. In addition,
Large effect of water repellency when using fluorinated carbon silane adsorbent
It is particularly preferable because it has good electrical insulation properties.

As described above, the lower electrode 2 of the superconductor is provided on the substrate 1, the hydrophilic group is formed thereon, and then a plurality of chlorine-silicon chemical bonds (-SiCl _n X _3-n group, n
= 2 or 3, X is a functional group) and a chlorosilane-based adsorbent gas containing a linear carbon chain having a functional group) is reacted to adsorb the monomolecular film precursor, followed by hydrolysis and dehydration condensation reaction-
A monomolecular adsorption film 3 (barrier layer) such as Si (O-) ₃ is formed. The monomolecular adsorption step is preferably performed at least twice. An upper electrode 4 of a superconductor is formed on the surface layer of this barrier layer to form a Josephson element 5.

Specific examples will be described below. Example 1 FIG. 2 is a process sectional view showing an example of a process for manufacturing a Josephson device of the present invention. A low resistance Si single crystal substrate is used as the substrate 11, and an oxide film of 400 n is formed thereon by thermal oxidation.
What was formed in m thickness was used. After fixing the substrate 11 in a vacuum chamber and evacuating it to 10 ⁻⁶ Torr or less, a Nb thin film with a thickness of 150 nm is formed by an electron beam evaporation method or the like to form a superconducting lower electrode 12. After that, a reactive gas of oxygen and hydrogen with a mixing ratio of 2: 1 was introduced near the surface of the lower electrode 12 so that the pressure near the surface of the lower electrode 12 was 10 ⁻³ To.
While performing differential evacuation to about rr, ultraviolet rays are radiated from a mercury lamp provided in the chamber to form a hydroxyl group 15, which is a hydrophilic group, on the surface of the lower electrode 12. It is also effective to use water vapor as the reactive gas. For convenience, it is possible to use the water vapor contained in the air by introducing it into the atmosphere. However, since it causes contamination, it is preferable to use an inert gas such as Ar bubbled in pure water. Is good. In addition to the hydroxyl group, examples of the hydrophilic group include groups having active hydrogen such as an amino group. In the case of an amino group, it can be treated by supplying ammonia gas for reaction. When the reaction is completed, the reactive gas is stopped, the vacuum exhaust is performed to remove the reactive gas, and when the vacuum degree of 10 ^-6 Torr or less is reached, the chemical adsorbent 16 is carried to the substrate surface in a vapor phase state. ,
A chemical reaction is caused to be adsorbed on the surface of the substrate. In the case of a chemical adsorbent with a high vapor pressure at room temperature, it is sufficient to carry the chemical adsorbent to the substrate surface using an inert gas such as dehydrated and dried carrier gas such as argon or nitrogen, but it is a liquid state at room temperature. In the case of an adsorbent, it is supplied as vapor by heating it above the boiling point, or an inert gas such as dehydrated and dried argon or nitrogen is used as a carrier gas and bubbled through a liquid chemical adsorbent. As a result, it is supplied onto the surface of the substrate in a vapor phase state. In any case, it is important to remove water extremely in order to prevent the chemical adsorbent 16 from reacting with water to form a polymer. In the case of a chemical adsorbent that is in a solid state at room temperature, it can be supplied as a molecular beam gas by putting it in a crucible and evaporating it by heating it to a temperature above its boiling point. CF ₃ as a silane-based adsorbent that is the chemical adsorbent 16
When (CF ₂ ) ₇ (CH ₂ ) ₂ SiCl ₃ is used, since it is in a liquid state at room temperature, it is placed in a sealed container and dehydrated and dried, and an inert gas such as argon or nitrogen is used as a carrier gas. Bubbling is carried out through a chlorosilane-based adsorbent in a hermetically sealed container, and this gas is carried by a thin pipe to the surface of the substrate and supplied. The chemical adsorbent 16 carried on the surface of the lower electrode 12 undergoes dehydrochlorination reaction between chlorine of the —SiCl group of the chlorosilane-based adsorbent and the hydroxyl group 15 on the surface of the lower electrode 12 by adsorption for about 10 to 30 minutes. Then, by hydrolyzing and dehydrating and condensing, the lower electrode 1
The siloxane bond shown in (Chemical formula 1) is generated over the entire surface of 2, and the chemisorption monomolecular film 17 is formed through this (FIG. 3).

[0023]

[Chemical 1]

Since the above reaction is carried out in the gas phase (mainly under reduced pressure), water molecules and hydrogen chloride molecules generated during the chemical reaction are rapidly carried away from the substrate surface by diffusion,
It is possible to prevent the occurrence of a secondary chemical reaction such as the slowing of the adsorption reaction and the erosion of the lower electrode 12 by the residual hydrogen chloride molecule after the device is manufactured. This is because, in the gas phase, the density of the heat-moving molecules, which hinder the diffusion of reaction products, is extremely lower than that in the liquid phase, so that the diffusion takes place very quickly. Is a characteristic of chemisorption. In the chemisorption, a hydrophilic group having active hydrogen is used as a reaction site. Therefore, when the active hydrogen disappears due to the adsorption, the adsorption reaction is automatically terminated and the chemisorption monomolecular film 17 is obtained. Since the molecular density of the chemisorption film 17 depends on the density of hydrophilic groups on the surface of the lower electrode 12, the hydrophilic treatment after forming the lower electrode 12 is important. After that, the supply of the chemical adsorbent gas is stopped, the gas is exhausted to about 10 ⁻⁶ Torr or less, and the extra chemical adsorbent physically adsorbed on the chemical adsorption film monomolecular film 17 by the Van der Waals force. Is removed and removed. At this time, the desorption progresses faster and is effective by heating the substrate 11 to a temperature at which the monomolecular adsorption film 17 is not decomposed, for example, about 200 ° C. while vacuum evacuation. When the removal of the excess chemisorbent is completed, only the chemisorption monomolecular film 17 remains on the lower electrode 12. Since the chemical adsorption monomolecular film 17 has the same molecular length, the barrier layer 3 having a uniform film thickness can be obtained. The thickness of the chemisorption monomolecular film 17 is about 15 angstroms due to the molecular structure. On top of this, a 150 nm-thick N
b. A thin film is formed to form the superconducting upper electrode 4 to form a Josephson junction. Since the chemisorption monomolecular film 17 was extremely strongly chemically bonded, it was not peeled at all. Further, neither the lower electrode 12 nor the upper electrode 4 was damaged. This Josephson junction is cut out by a conventional fine processing technique to form a minute Josephson element 5.

Next, in the Josephson device of the first aspect of the present invention, an embodiment using a chemisorption monomolecular cumulative film for the barrier layer 3 will be described. Carrying the chemical adsorbent in the gas phase to the lower electrode surface and causing the chemical adsorption on the lower electrode surface is the same as in the specific example 1, but a plurality of chlorine-silicon chemical bonds (-SiCl) are used as the chemical adsorbent. _n X _3-n group, n = 1, 2,
3, X is a substance containing a linear carbon chain having a functional group), and an inert gas such as dehydrated and dried argon or nitrogen is used as a carrier gas, and bubbling is performed by passing through this liquid. It is conveyed to the lower electrode surface in a phase state and exposed to the lower electrode surface for chemical adsorption (adsorption step). Then, unreacted chlorine physically adsorbed on the surface of the lower electrode
The substance containing the chemical bond of silicon is evacuated again to desorb and remove (removal step). Then, the unreacted chlorine-silicon chemical bond of the substance containing the chemically adsorbed chlorine-silicon chemical bond is reacted by introducing water vapor to the lower electrode surface or introducing hydrogen gas and oxygen gas to the lower electrode surface. Then, ultraviolet rays are simultaneously irradiated to react with each other to form a silanol group, thereby producing a monomolecular film. A process including such a process will be referred to as a monomolecular adsorption film forming process. Since a large number of hydroxyl groups are present on the surface after the monomolecular adsorption film forming step, the chemical adsorption monomolecular film can be accumulated by repeating the monomolecular adsorption film forming step a plurality of times (chemical adsorption film forming step). Even in this way, a monomolecular film can be formed. Further, after forming the chemisorption monomolecular film in this way, by heating a silane-based adsorbent containing carbon fluoride, or by bubbling with a dehydrated and dried inert gas such as argon or nitrogen as a carrier gas. It is possible to expose the surface of the chemical adsorption film in a gas phase, chemically react with silanol groups of the chemical adsorption film to form a siloxane bond, and accumulate the chemical adsorption monomolecular film to form a monomolecular film. It is preferable to employ such a method because a silane-based adsorbent containing fluorocarbon can be chemically adsorbed at a high density even when the surface of the lower electrode has few hydrophilic groups exposed on the surface.

As the material having this chlorine-silicon chemical bond,
For example, SiCl_Four, SiHCl₃, SiH₂Cl
₂, Cl- (SiCl₂O)_n-SiCl₃, H_l(R
¹) _3-lSi (R²)_nSiCl_m(R³)_3-mEtc.
Generally, the one with more Cl-Si bonds is silane-based.
It is preferable since the adsorbent can be chemically adsorbed at a high density. However, the formula
Where n is an integer, l and m are integers of 1 to 3, R¹And R³Is
Lower alkyl group, R²Is a methylene group having 1 or more carbon atoms
It In particular, SiC as a substance containing a chlorine-silicon chemical bond
l_FourIs used, the molecule is small and the activity for hydroxyl groups is large.
The effect of making the surface of the lower electrode uniform and hydrophilic is great.
It's good.

Embodiment 2 FIG. 4 is a process sectional view showing another embodiment of the manufacturing process of the Josephson device of the present invention. The superconducting lower electrode 12 is formed on the substrate 11, a reactive gas is introduced, and a hydroxyl group 15 is formed as a hydrophilic group on the surface thereof. Then, the reactive gas was stopped, and the chamber was evacuated again to about 10 ^-6 Torr to obtain a plurality of chlorine-silicon chemical bonds (-SiCl) as a chemical adsorbent.
_{nX 3−n} group, n = 1, 2, 3 and X is a functional group) A substance containing a linear carbon chain, in particular, SiCl ₄ is used as the substance 26 containing a trichlorosilyl group and placed in a sealed container. Then, a carrier gas, such as dehydrated and dried inert gas such as argon or nitrogen, is passed through SiCl ₄ in a sealed container for bubbling, and this gas is carried to the lower electrode surface by a thin pipe for about 10 minutes. To the extent that the adsorption reaction occurs. As shown in FIG. 4, a dehydrochlorination reaction occurs between the hydrophilic hydroxyl group 15 formed on the surface of the lower electrode 12 and the chlorine atom of the substance 26 containing a trichlorosilyl group, and a chlorosilyl monomolecule of the substance 26 containing a trichlorosilyl group. Membrane 27
Is formed. Thus, when SiCl ₄ is used as the substance 26 containing a trichlorosilyl group, a dehydrochlorination reaction occurs on the surface of the lower electrode 12 even if only a small amount of OH groups 15 are present on the surface of the lower electrode 12 (Chemical Formula 2 and / or Chemical 3)
The molecule is fixed to the surface via the -SiO- bond as in. At this time, in general, unreacted SiCl ₄ is also present on the chlorosilyl monomolecular film by physical adsorption, and therefore, the unreacted SiCl ₄ is desorbed and removed by evacuation again. Substrate heating at this time is also effective.

[0028]

[Chemical 2]

[0029]

[Chemical 3]

Next, the unreacted chlorine-silicon chemical bond of the chemically adsorbed chlorosilyl monomolecular film 27 is introduced into the lower electrode surface to react with it, or hydrogen gas and oxygen gas are introduced to the lower electrode surface. While being introduced and irradiated with ultraviolet rays to react with each other to form a silanol group, a siloxane monomolecular film 28 of (Chemical Formula 4 and / or Chemical Formula 5) is obtained on the surface of the lower electrode 12 as shown in FIG.

[0031]

[Chemical 4]

[0032]

[Chemical 5]

Since the siloxane monomolecular film 28 formed at this time is completely bonded to the surface of the lower electrode 12 through the chemical bond of -Si-O-, it does not peel off.
In addition, the obtained siloxane monomolecular film 28 has Si on the surface.
It has a large number of —OH bonds, and about three times the number of initial hydroxyl groups is generated.

Next, the chlorosilane-based absorber described in Example 1 was used.
Adhesive CF₃(CF₂)₇(CH₂) ₂SiCl₃Using
Chemical adsorption. It was dehydrated and dried in the same manner as in Example 1.
Inert gas such as argon or nitrogen is used as carrier gas
Then, pass it through a chlorosilane-based
Ring the gas, and use a thin pipe to scan this gas on the surface.
Carry to the substrate 11 on which the xanthane monolayer 28 is formed, 1
It is exposed for 0 to 30 minutes to perform chemisorption. Then the adsorption
The supply of agent gas is stopped and the system atmosphere is changed to N₂Such as gas
Hydrolysis by replacing with active gas and then supplying steam
Then, by dehydration condensation, the siloxane unit
A bond of (Chemical Formula 6) is generated on the surface of the molecular film 28, which is shown in FIG.
As described above, the chemisorption monomolecular film 29 containing fluorine is formed in the lower layer.
Lower part in a state of being chemically bonded to the siloxane monomolecular film 28a of
Approximately 20 angstroms over the entire surface of the electrode 12
A monomolecular film can be formed with a film thickness.

[0035]

[Chemical 6]

The chemisorption monomolecular film was not peeled at all even after the peeling test. Then, Example 1
Similarly to the above, the superconducting upper electrode 4 is formed to form a Josephson junction, and fine processing is performed to form a Josephson element. The obtained characteristics were small in leak current, and were equal to or higher than those in Example 1. this is,
It is considered that this is due to the fact that the chemisorption monomolecular film 29 is slightly thick and has a high density.

The example 1 shows the case of one monolayer film, and the example 2 shows the case of forming one layer of the siloxane monolayer film and accumulating one layer of the silane-based adsorbent layer containing fluorine. However, the effect of the chemisorption monomolecular film, which is the material of the barrier layer 3 of the Josephson device of the present invention, does not change even if it is accumulated not only in one layer but in multiple layers. It is extremely useful that a monomolecular film having a desired uniform film thickness can be obtained by appropriately selecting the chain length of the adsorbed monomolecule or by accumulating the chains.

Furthermore, in the above embodiment, fluorocarbon black is used.
CF as a rusilane-based adsorbent₃(CF₂)₇(C
H₂)₂SiCl₃Was used, but CF₃-(CF₂)_p
-(R) _m-SiCl_nX_3-nChlorcilla represented by
For example, vinylene group (-CH = C
H-) can be added or incorporated to form a monomolecular film.
Because it can be cross-linked by electron beam irradiation of about 5 megarads,
It is also possible to improve the hardness of the monomolecular film.

The above-mentioned fluorocarbon-based adsorbent is also used.
CF besides₃CH₂O (CH₂)₁₅SiCl₃, C
F₃(CH₂)₂Si (CH₃)₂(CH₂)₁₅SiC
l₃, F (CF₂)_Four(CH₂)₂Si (CH₃)
₂(CH₂)₉SiCl₃, CF ₃COO) (CH₂)
₁₅SiCl₃, CF₃(CF₂)_Five(CH₂)₂SiC
l ₃Such as trichlorosilane-based adsorbents such as CF
₃CH₂O (CH₂)₁₅Si (CH₃)₂Cl, CF₃
(CH₂)₂Si (CH₃)₂(CH₂)₁₅Si (CH
₃)₂Cl, CF₃CH₂O (CH₂)₁₅Si (C
H₃) Cl₂, CF₃COO (CH₂)₁₅Si (C
H₃)₂A chlorosilane-based adsorbent such as Cl was available.
Also CF₃(CF₂)₇(CH₂)₂Si (OCH₃)
₃, CF₃CH₂O (CH₂)₁₅Si (OCH₃)₃etc
Alkoxysilane-based adsorbent also heats the adsorbent solution
As a result, the same effect was obtained. CH₃(CH₂)₉
SiCl₃, CH₃(CH₂)₁₅SiCl₃, CH₃C
H₂O (CH₂)₁₅SiCl₃, CH₃(CH₂)₂S
i (CH₃)₂(CH₂)₁₅SiCl₃Hydrocarbon groups such as
Similarly, with a chlorosilane-based adsorbent having
A chemisorption monolayer can be formed in the air. Next, the present invention
A method of manufacturing the Josephson device will be described. In Figure 7
The manufacturing process sectional drawing is shown. Hydrophilic groups on the surface of the lower electrode 12
Until the formation, it is the same as the concrete examples 1 and 2 described above.
Is. However, in this case, multiple chlorine-silica
Elementary chemical bond (-SiCl_nX_3-nGroup, n = 2 or 3,
X is a chlorosilane containing a linear carbon chain having a functional group)
A system adsorbent is used as a chemical adsorbent. Specifically, CF
₃(CF₂)₇(CH₂)₂SiCl₃Etc. are used. about
After adsorption for about 30 minutes, 10^-6Below Torr
Chemical adsorbent that was not chemically adsorbed after evacuation
Is removed from the surface of the lower electrode. When removing this desorption
Substrate heating is an effective method as described in the above specific examples.
You don't have to. After desorption / removal is completed,
Chlorosilane adsorbent is siloxane on the surface of electrode 12.
The adsorbed monolayer 31 chemically adsorbed by the bond 18 is formed.
Be done. However, the adsorbed monolayer 31 generally has a metal raw material.
There are some pinholes 32 that allow the child to pass through.
When the superconducting electrode 4 is formed by vapor deposition or the like, the lower electrode 1
2 connected in a micro-bridge shape,
New devices, devices with weak coupling characteristics, etc.
This causes deterioration of the Sefson characteristics and variation in the characteristics. This
This is the density of hydroxyl groups formed on the surface of the lower electrode 12.
Occurs when is not high enough. The present inventors
Review chemisorption process to eliminate small pinholes
And find a new, effective way to overcome this problem
It was. As previously mentioned, multiple chlorine-silicon chemistries at one end
Bond (-SiCl_nX_3-nGroup, n = 2 or 3, X is a government
Adsorption of chlorosilanes containing linear carbon chains with functional groups)
Since the agent is used as a chemical adsorbent, the lower electrode 12 is chemically
The unreacted chlorine-silicidation is formed on the adsorbed adsorption monolayer 31.
There will be more than one scientific bond, so oxygen
UV rays are introduced by introducing a reactive gas that is a mixed gas of hydrogen and hydrogen.
Irradiate and react to form silanol groups (Fig.
8). As a result, a new
1 or more hydroxyl groups 33, which are adsorption sites, (in the case of FIG. 8)
2) will be added (hydrophilization treatment). There
Is adsorbed when adjacent adsorbed single molecules are close to each other.
Single molecules are bound to each other by a siloxane bond. This
Thus, the adsorption monomolecular film 34 is formed. Then anti
Remove the reactive gas and use the same chemisorbent again to vapor phase
Chemisorption is performed inside. Chemisorption is a reaction site
Occurs selectively only where hydroxyl groups are present,
There are no hydroxyl groups on the already adsorbed monolayer.
Therefore, cumulative adsorption does not occur on this. On the other hand, adsorption
Around the pinhole 32 of the monomolecular film, the above-mentioned hydrophilic property is provided.
By the treatment, hydroxyl group 33 is formed in the portion adjacent to the lower electrode 12.
Because it is exposed, the linear chemical adsorbent has a pinhole 3
It penetrates into the area of 2 and chemically bonds with this hydroxyl group 33 and is absorbed.
Thus, the chemisorption monomolecular film 35 is formed (FIG. 9). to this
As a result, the number of pinholes decreases. This hydrophilic treatment and re-treatment
By repeating the adsorption process, the density of adsorbed molecules increases
However, the number of pinholes decreases accordingly. Adsorption
The child density saturates when the pinhole disappears. other
The lower part of the single molecule 36 additionally adsorbed by the re-adsorption process
The height from the surface of the electrode 12 is the monolayer first adsorbed
It is only a few angstroms higher than 37,
The influence on the dispersion of the characteristics of the Josephson device is light.
It is fine. By manufacturing in this way, monomolecular adsorption film
Excellent barrier layer with high molecular density and few pinholes
However, Joseph can be easily formed and has less variation in characteristics.
Since the device can be manufactured, its effect is extremely large.
Yes.

After the hydrophilic treatment after forming the lower electrode 12, a monomolecular film having a siloxane bond at both ends and an active hydroxyl group capable of forming a siloxane bond, as described in Specific Example 2, was used alone. Alternatively, even after cumulative formation, the same effect as above can be expected even if hydrophilic treatment is performed with a reactive gas and chemical adsorption is performed. In this case, a plurality of adsorbed gases are required, which complicates the manufacturing apparatus, but is characterized in that the film thickness of the barrier layer can be adjusted in units of several angstroms.

FIG. 10 shows an example of current-voltage characteristics of the created Josephson element. As shown in the figure, good tunnel junction Josephson device characteristics are obtained. It is stable even after repeated temperature cycles from room temperature to liquid helium temperature, and there is no change in its characteristics.

In the description of this embodiment, Nb was used as the superconducting material, but it is not limited to this and it is clear that a compound superconductor such as NbN may be used. is there. In addition, the superconducting lower electrode has a Y-Ba-
Cu-O system, Bi-Sr-Ca-Cu-O system, Bi-
Pb-Sr-Ca-Cu-O system, or Tl-Ca-B
It is also possible to use an oxide high temperature superconductor such as an a-Cu-O system. Further, although only the electron beam evaporation method has been described as the method for forming the superconducting electrode, the method is not limited to this, and other methods such as sputtering method, resistance heating evaporation method, ion beam sputtering method, reactive evaporation method, laser ablation method are also available. It goes without saying that such a method is possible.

[0043]

As described above, in the Josephson device of the present invention, since the chemisorption monomolecular film chemically bonded to the superconducting electrode is used for the barrier layer, it is mechanically stable and the chemisorption monomolecule is formed. Since the film thickness is uniform, a barrier layer of several nanometers with uniform characteristics can be realized, and a Josephson device with high critical current density, uniform characteristics and rich reproducibility can be realized.

In the Josephson device manufacturing method of the present invention, after adsorption is performed using a molecule containing a linear carbon chain having two or more highly reactive chlorine-silicon chemical bonds only at one end, Since the unreacted chlorine-silicon chemical bond is replaced with a hydroxyl group to increase the number of adsorption sites, a chemical adsorption film can be formed at a high density and a pinhole-free barrier layer can be manufactured. Therefore, the Josephson device having the tunnel junction type characteristic can be easily manufactured with a small variation and a high yield, so that the economical effect thereof is extremely large. Further, since the chemical adsorption reaction is caused in the gas phase atmosphere, a chemical adsorption film with less contamination can be obtained, and since the superconducting electrode is continuously formed in the same vacuum container, the effect of reducing contamination is great. , Interface control is easy.

[Brief description of drawings]

FIG. 1 is a sectional structural view showing a first embodiment of a Josephson element of the present invention.

FIG. 2 is a sectional process conceptual diagram in which a substrate surface is enlarged to a molecular level, showing a manufacturing method in a first embodiment of a Josephson device of the present invention.

FIG. 3 is a sectional process conceptual diagram in which a substrate surface is enlarged to a molecular level, showing a manufacturing method of a Josephson device according to a first embodiment of the present invention.

FIG. 4 is a sectional process conceptual diagram in which the substrate surface is enlarged to a molecular level, showing a manufacturing method of a Josephson device according to a second embodiment of the present invention.

FIG. 5 is a conceptual sectional process diagram in which a substrate surface is enlarged to a molecular level, showing a method for manufacturing a Josephson device according to a second embodiment of the present invention.

FIG. 6 is a conceptual cross-sectional process diagram in which the substrate surface is enlarged to the molecular level in one example showing the method for manufacturing the Josephson device of the present invention.

FIG. 7 is a conceptual cross-sectional process diagram in which the substrate surface is enlarged to the molecular level in one example showing the method for manufacturing the Josephson device of the present invention.

FIG. 8 is a conceptual cross-sectional process diagram in which the substrate surface is enlarged to the molecular level in one example showing the method for manufacturing the Josephson device of the present invention.

FIG. 9 is a sectional process conceptual diagram in which the substrate surface is enlarged to the molecular level in one example showing the method for manufacturing the Josephson device of the present invention.

FIG. 10 is a current / voltage characteristic diagram in an embodiment of the Josephson device of the present invention.

[Explanation of symbols]

 1, 11 Substrate 2, 12 Lower electrode 3 Barrier layer 4 Upper electrode 5 Josephson element 15, 33 Hydroxyl group 16 Chemical adsorbent 17, 29, 35 Chemisorbed monolayer 18 Siloxane bond 26 Substance containing trichlorosilyl group 27 Chlorosilyl monolayer Molecular film 28, 28a Siloxane monomolecular film 31, 34 Adsorption monomolecular film 32 Pinhole

Claims (9)

[Claims] 1. A Josephson device including an upper electrode and a lower electrode made of a superconductor, and a barrier layer separating the two, wherein the barrier layer is a linear carbon chain containing a water-repellent group and silicon. A Josephson device, which is a chemical adsorption film to be formed, wherein the chemical adsorption film is fixed by a covalent bond to at least one surface of the upper electrode or the lower electrode facing each other. 2. The Josephson device according to claim 1, wherein the covalent bond is a siloxane bond. 3. The Josephson device according to claim 1, wherein the chemisorption film is covalently bonded to the surface through at least the siloxane-based inner layer film. 4. The Josephson device according to claim 1, wherein the water-repellent group is a fluorine-containing hydrocarbon group. 5. A method of manufacturing a Josephson device including an upper electrode made of a superconductor, a lower electrode, and a barrier layer separating the two, wherein a reactive gas is introduced after the lower electrode is formed on a substrate. Then, after forming a hydrophilic group on the surface of the lower electrode, or after forming a siloxane-based chemisorption inner layer film to form a hydrophilic group with a reactive gas, the reactive gas is removed and chlorine is added to one end. Chemical bond of silicon (-SiCl _n X
A chlorosilane-based adsorbent gas containing a linear carbon chain having a _3-n group, n = 2 or 3, and X is a functional group) is introduced on the surface of the lower electrode to cause an adsorption reaction to form a chemisorption precursor film. After that, the unreacted chlorosilane-based adsorbent gas is removed, and then a reactive gas is introduced to react with the unreacted chlorine-silicon chemical bond of the chemisorption precursor film to form a silanol group to form a chemisorption film. A method of manufacturing a Josephson device, characterized by the above. 6. The method for manufacturing a Josephson device according to claim 5, wherein the step of forming the chemisorption film is performed at least twice. 7. The method of manufacturing a Josephson device according to claim 5, wherein water vapor is used as the reactive gas. 8. Hydrogen and oxygen are used as the reactive gas, and at the same time when the reactive gas is introduced, the substrate surface is irradiated with ultraviolet rays to form a hydrophilic group on the surface of the lower electrode, or a chemical adsorption precursor film is formed. The method for producing a Josephson device according to claim 5, wherein a silanol group is formed by reacting with an unreacted chlorine-silicon chemical bond. 9. The chlorosilane-based adsorbent is CF _3- (C
F ₂ ) _p- (R) _m -SiCl _n X _3-n (p is 0 or an integer, m is 0 or 1, R is a methylene group having 1 or more carbon atoms, and a methylene group having 1 or more carbon atoms of a vinylene-containing group. , Either a methylene group having 1 or more carbon atoms of a silicon-containing atom or a methylene group having 1 or more carbon atoms of an oxygen-containing atom, X is a hydrogen atom,
The method for producing a Josephson device according to claim 5, wherein a lower alkyl group or a lower alkoxy group and n is 2 or 3).