JPH04113683A - Manufacture of thin film device - Google Patents

Abstract

PURPOSE:To obtain a thin film device which can operate a device at a critical temperature by providing an oxide superconductor layer containing Cu on a board, laminating a thin metal film of an element different from metal element contained in the superconductor layer on an oxide layer and a thin film to become the superconductor layer, and then annealing it. CONSTITUTION:An oxide superconductor layer 1 is formed on a board 1, then a masking 3 is placed on the layer 1, a thin metal film 4 is deposited on the layer 1 through the masking 3 in this state, and then annealed. As the oxide superconductor, for example, LB2Cu3O7-sigma such as YBa2Cu3O7-sigma, or oxide represented by Tl2Ba2Can-1Cu2n+4 is employed. The metal for forming the thin metal film includes, for example, Al, Ga, Fe, Co, Ni or Cr.

Description

[Detailed Description of the Invention] <Industrial Application Field> The present invention relates to a method for manufacturing a thin film device, and more specifically, a method for manufacturing a thin film device using an oxide high temperature superconductor, which is useful for Josephson elements and the like. It is related to.

<Prior art> Nb or Nb s, which has been studied in recent years
AlS type compounds (β
C as a superconductor to replace the superconductor with W-type crystal structure
Oxide superconductors containing a u-0 layer in their crystal structure are actively researched.

A typical material for such an oxide superconductor is Y
-Ba-Cu-0 system (critical temperature Tc>90K), B
i-5r-Ca-Cu system (critical temperature Tc -80~ll
0K), or the Tfl-BaCa-Cu-0 system (critical temperature Tc -90 to 120K).

The most important technique when using these materials as a Josephson element, which is an electronic device, is the formation of a Josephson junction. This Josephson junction is formed by a vapor deposition method, a sputter deposition method, or a laser ablation method.

However, it has been confirmed that the correlation length of the above-mentioned materials is extremely short, and the material surface is easily deteriorated.

In addition, when a Josephson junction is formed by stacking thin films of these materials with an interlayer intervening to form a gap, if the lattice matching between the superconducting material and the interlayer is poor, the adjacent superconducting layer may Due to properties deterioration and leakage current generated from the intermediate layer, S/N/S (superconductor/normal conductor (conductor)/superconductor) junction with good reproducibility may not be obtained. Alternatively, even in the case of S/I/S (superconductor/insulator/superconductor) junction, there are drawbacks such as leakage current and failure to obtain superconducting coupling.

In order to solve these drawbacks, for example, in the case of a stacked thin film device, the following methods (a) to (C) have been proposed.

(a) A method in which an insulating film is formed on an oxide superconductor, and then a conventional (phonon type) superconductor (for example, Nb or Nb-based alloy, pb or pb compound) is laminated.

(b) Oxygen-poor material of metal superconductor as an intermediate layer on oxide superconductor, or Mg usually used for substrate
A method of stacking materials such as 0SSrTiO and ZrO2, and then stacking a superconductor on top of them.

(C) An insulator layer is formed on the oxide superconductor by replacing rare earth elements and alkaline earth metals in the oxide superconductor with other elements, and an oxide layer is formed on the insulator layer. How to stack superconductors.

<Problem to be solved by the invention> However, in the case of method (a) above, since a conventional superconductor is used, there is a problem that the device can only be operated at the temperature of liquid helium. be.

In addition, in method (b), when a metal superconductor with low oxygen content is used as the intermediate layer, it is difficult to obtain a sharp interface due to poor controllability of oxygen diffusion during annealing, and it is difficult to obtain a sharp interface when the intermediate layer is made of a metal superconductor with low oxygen content. When using materials, M
There is a problem in that it is difficult to obtain a film with good characteristics due to the diffusion of g and the like.

Furthermore, in method (C), the bond between the Cu-0 layer, which exhibits superconducting properties, and rare earth elements, etc. is weak, so in order to change from superconducting properties to insulating properties, a large amount of the above substitution (50% or more) is required.
The problem is that it has to be done.

On the other hand, in microbridge-type thin film devices, in addition to the above-mentioned methods, a method is used in which the superconducting film is destroyed or removed by irradiation with ultraviolet light or ion beams, thereby forming a non-superconducting portion. There is.

In the case of ultraviolet light, the superconducting properties are difficult to completely destroy with normal light sources, so it is necessary to use a high-power source such as an excimer laser, and in the case of ion beams, it is also necessary to use gas ions. .

However, these patterns using ultraviolet light irradiation using an excimer laser or etching the superconducting film using gas ions have poor productivity and are difficult to apply to industrial mass production.

<Means for Solving the Problems> In order to solve these problems, the present inventor has conducted extensive research and developed S.
As a normal conductor or insulator used for the /N/S bond or the S/I/S bond, some of the elements constituting the above oxide superconductor may be a group II group b subgroup element of the periodic table such as Zn. ,
Group III group b subgroup elements of the periodic table, such as Aβ, Ga, or Fe.

It has been found that by substituting a transition element other than Cu such as Co, Ni, or Pt, a normal conductor layer or an insulator layer having a critical temperature Tc lower than the device operating temperature can be constructed.

Further, a thin film device having such a laminated structure can be produced by laminating the metal thin film on a thin film of an oxide superconductor layer formed on a substrate, and then subjecting it to an annealing treatment.
It has been found that this can be obtained by laminating the above metal thin film on a thin film composition that becomes an oxide superconductor by annealing and then annealing the film.

The present invention is based on the above knowledge, and is a method for manufacturing a thin film device, which comprises providing an oxide superconductor layer containing Cu on a substrate, and providing an oxide layer in contact with the oxide superconductor layer. wherein the oxide layer is formed on the oxide superconductor layer or on the thin film that becomes the oxide superconductor layer by annealing, and is different from the metal element contained in the oxide superconductor layer. This is a method for manufacturing a thin film device, the gist of which is that the thin film device is obtained by stacking elemental metal thin films and then subjecting them to an annealing treatment.

The oxide layer is the same as the oxide superconductor or Cu
A part of the elements constituting other oxide superconductors containing This is an oxide layer substituted with an element.

In the present invention, the oxide superconductor is specifically, for example,
LB2CuO, -(L
: rare earth element, B: alkaline earth), Bi Sr
CaCu O, BiSr CaCu OBi
Sr Ca2 28-δ' 2 2+y
Cu O or B125r2Ca2Cu2-y
3 10 0 Bi B B Cu 031
0-δ' 2 lx Ily n 2n
+4 (x+y n+1, n-1, 2, 3) or Tρ Ba Ca Cu2 2
An example is an oxide containing a two-dimensional plane of Tn and 2n+4 Cu-0, represented by n-1n O (n-1,2,3).

Further, the metal forming the metal thin film must contain at least the metal elements contained in the oxide superconductor layer, including elements of Group II b subgroup of the periodic table such as Zn, An,
Group III group b subgroup elements of the periodic table such as Ga, or Fe,
Transition elements other than Cu such as Co, Ni, and Pt, especially Aρ,
Ga.

Fe, Co, Ni or Cr are used.

Specific methods for laminating metal thin films include known physical vapor deposition methods and chemical vapor deposition methods such as vacuum deposition, ion beam deposition, and sputter deposition.

Annealing is normally performed under known conditions. For example, in the case of YBaCuO (rare earth element) 2 37 -δ, firing may be performed at 900 to 970°C for 0.5 to 24 hours. Also B 12 S r 2 Ca CLJ
In the case of 20 g (Bi type), it is 0 at 800-890℃.
．． It is sufficient to bake for 5 to 24 hours. In either case, cooling is performed by cooling to about 600° C. over about 24 hours, and then allowing it to cool.

Further, when forming a Josephson bond using the manufacturing method of the present invention, an oxide superconductor layer containing Cu is further provided in contact with the oxide layer, that is, between two oxide superconductor parts. The structure may be such that the oxide layer is disposed on the oxide layer.

On the other hand, it is preferable that the oxide superconductor layer constituting the thin film device has a C-axis orientation, or an A-axis or B-axis orientation with respect to the substrate, and it is further preferable that no grain boundaries exist in each of these partitions. .

The thickness of each layer of the thin film device is preferably as thin as possible, as long as a -like film is formed and the thickness is similar to that of the bulk. Specifically, 30 to 5,000 people were involved in the oxide superconducting layer, and 2 people each in the oxide layer (insulator layer, normal conductor layer).
0 to 1000 people will be selected.

An oxide superconductor layer on a substrate or a thin film that becomes an oxide superconductor layer by annealing can be formed by conventional film deposition methods that form a flat, -like film, such as molecular beam evaporation (MBE),
Electron beam evaporation method.

They are formed by sputter deposition, laser abrasion, etc.

The composition of the thin film that becomes an oxide superconductor layer by annealing may be almost the same as the composition of the oxide superconductor layer, that is, it may have a slight excess of 0 or may contain F.

FIGS. 1A to 1C show an example of forming a pair of microbridge type thin film devices. When forming an insulating layer or a normal conducting layer in contact with an oxide superconductor layer in this thin film device, first, as shown in FIG. A thin film composition (which will become an oxide superconductor layer) is formed, and then, on top of this oxide superconductor layer 1, for example,
A masking 3 having the shape shown in B) is placed on the oxide superconductor layer 1. In this state, a thin metal film 4 is deposited on the oxide superconductor layer 1 through the masking 3 as shown in FIG. 1C, and then annealing is performed. method can be adopted.

Fig. 2 (A) shows an example of a Josephson element consisting of a microbridge type thin film device, in which two superconductor layers (superconductor films) are formed on the left and right sides of the substrate plane. A structure in which the connecting part at the center of S is made thinner than the superconductor layers S on both sides or made thinner by the method described above, and normal conductor layers (normal conductor films) N are provided above and below this connecting part in contact with each other. It is.

In the above structure, the normal conductor layer N may be only a part of the superconducting portion of the superconductor layer S where the bonding portion becomes thin. Figure 2 (B) is an example of this, in which the hole provided at the narrowed part of the bonding part of the superconductor layer S is made non-superconducting (in the figure, it is made normal conductor to form the normal conductor layer N). , the so-called SQUIDt
This is an example of M construction.

The above-mentioned narrowed superconducting portions and hole portions may be obtained by forming an insulator layer around them by using the above-described masking method or conventional ultraviolet or ion beam irradiation.

In addition to the structure described above, for example, in a stacked thin film device, another film may be formed on the thin film device to express an additional function, or a known buffer layer (Z) may be formed between the superconductor layer and the substrate. It is also possible to have a structure in which a material (e.g., rO2, MgO, etc.) is inserted. Furthermore, it is of course possible to provide a protective film if necessary.

<Function> Through the above annealing treatment, a thin film device in which an oxide layer is formed on the oxide superconductor layer is obtained.

This is due to the fact that Cu in the constituent elements of the oxide superconductor is replaced by the metal element in the metal thin film due to the annealing treatment, or oxygen in the constituent elements is taken away by the metal element, according to the consideration of oxide reduction potential. It is assumed that this is due to the reaction that occurs.

This oxide layer has a lower critical temperature than the oxide superconductor with which it is in contact, the critical temperature Tc can be easily controlled, and furthermore, it has good crystallinity and lattice matching with the oxide superconductor layer. Therefore, by providing this oxide layer, it is possible to obtain a thin film device that does not have the above-mentioned drawbacks and problems and can be operated at the critical temperature of the oxide superconductor constituting the device.

Furthermore, the reaction between the metal thin film and the oxide superconductor during the annealing process is extremely rapid, and the metal elements are evenly distributed in the film thickness direction! Confirmed by MMS (secondary ion mass spectrometry).

Furthermore, by adopting the method described above in which a metal thin film is laminated and then subjected to an annealing treatment to obtain an oxide layer from this metal thin film, even when forming a non-superconducting portion in a microbridge type thin film device, the above method can be achieved. can be easily applied as

<Example> Examples will be described below.

Powders of oxides of SrO, CaO, BiO, and CuO are mixed in a ratio of metal elements of 2:2:2:3, and Mn, W, Ni, and V are mixed therein.

Powders of oxides of Cr, Fe, Co, and Zn were mixed in appropriate proportions according to the composition of metal elements, and these were ground and further mixed.

Then, on a substrate consisting of Mg0(1(1)), this mixture was calcined at 800°C for 5 hours, and then at 850°C.
A thin film was formed on the substrate by baking in air at ~870°C for 24 hours and cooling at 50°C/hr.

When this thin film was examined by X-ray diffraction, it was found that BiS'2Ca is an oxide superconductor with a Bi-based 8OK phase crystal structure.
It was confirmed that it was Cu208.

Figure 3 shows that in this thin film, part of Cu is replaced with MnW, Ni,
This shows the decrease in critical temperature Tc (K) when X (96 atoms) is substituted with elements such as V, Cr, Fe, Co, and Zn. By changing the amount of substitution of these elements, the critical temperature Tc can be lowered. It can be seen that the control can be easily carried out. Incidentally, in FIG. 3, white circles indicate areas where there is no non-superconducting component.

Next, by the same method as above, BiS "2C", which is an oxide superconductor with a Bi-based high Tc phase crystal structure
A thin film made of a2Cu301o was formed.

In this thin film, the critical temperature T when a portion of Cu is replaced by X (96 atoms) with elements such as W and Cr
Changes in c (K) were investigated.

The results are as shown in FIG. 4, and it was found that the critical temperature Tc can be easily controlled by changing the amount of substitution of the above elements as in Example 1.

The above are examples of Bi-based oxide superconductors, or for example Y
It has been confirmed that the critical temperature Tc can be similarly easily controlled in the BCO system by replacing elements such as Co and Fe.

From these experimental results, it is expected that if sufficient matching is achieved in the laminated structure, it will work well as an S/N/S coupling.

Example 1 Oxygen gas O: nitrous oxide gas N20 was mixed with a gas mixture in the ratio of 9=1 (in an atmosphere of 1'torr, using a combination of electron beam and resistance heating with a multi-source evaporation device,
Y on a substrate made of S r T I O3 (100),
Co-deposited Cu and Ba to a thickness of 500 YBa
CuO was laminated, and 237-δ CO was further deposited thereon to a thickness of 200 nm. The deposition rate was 1 person/gfn, and the substrate temperature was 850°C.

The above thin film device was held under an oxygen partial pressure of 20 Otorr for 5 hours, and then cooled at 30° C./hour.

When we measured the in-plane superconducting properties of the obtained thin film, we found that the critical temperature Tc<4, the superconducting properties disappeared due to the Co-containing layer, and it was found that the diffusion at the interface was sufficiently high. .

Example 2 Under the same conditions as Example 1, BiO, SrOCab, C
By co-evaporating u onto a substrate made of Mg0(100),
A thin film of Bi25"2CaCu2ox (500 people) was prepared. The substrate temperature was 75 (1"c).

This thin film was subjected to X-ray diffraction. This X-ray diffraction image is as shown in FIG. 5, and showed the C-axis orientation of the Bi-based 80 phase. Furthermore, the current characteristics within the city in this thin film are as shown in FIG.

On the above film, 200 layers each of Ag, Cr, Ni, and Fe were laminated at room temperature, and heat treated at 800° C. for 1 hour. Ag
Superconducting transitions were no longer observed outside the amount of laminated films. In particular, the increase in resistance due to Cr was remarkable.

Furthermore, B l 2 S r 2 C produced in the same manner
8+δ Cr, Fe, and Mn were deposited on aCuO through 200 evaporation ports each through masking of a predetermined shape, and then 8
A micro bridge as shown in Fig. 2 (^) was prepared by heat treatment at 00°C. The bridge width was 100 μm. A resistance temperature curve almost the same as that shown in FIG. 6 was obtained, and superconducting transition also occurred at 80°C.

On the other hand, the resistance value increased by more than one order of magnitude, indicating that the desired bridge structure was obtained, and that it could be used as a weakly coupled superconducting device.

<Effects of the Invention> As described above, according to the present invention, there is provided a method for manufacturing a thin film device that does not have the drawbacks and problems of the prior art described above and can be operated at the critical temperature of the oxide superconductor that constitutes the device. can be provided.

[Brief explanation of drawings]

Figures 1 (A) to (C) are explanatory diagrams of the manufacturing process of a thin film device according to the present invention, Figures 2 (^) and (B) are explanatory diagrams of a microbridge type thin film device according to the present invention, FIG. 3 is a graph showing the decrease in the critical temperature Tc in the Bi-based 8 (IK phase) oxide according to the present invention, and FIG. 4 is a graph similarly showing the decrease in the critical temperature Tc in the Bi-based Tc high phase. , FIG. 5 is a graph of the X-ray diffraction results of the laminated film obtained in Example 2, and FIG. 6 is a graph showing the in-plane current characteristics of this film. 1... Superconductor film, 2 ...Substrate, 3.. Masking, 4.. Metal thin film, S.. Superconductor layer, N.. Normal conductor layer. Patent applicant: Mitsubishi Kasei Corporation Agent Yuki Omata
Male Diagram (A) Diagram (B) Diagram (C) 1 good (Kl

Claims (1)

[Claims] 1. An oxide superconductor layer containing Cu is provided on a substrate,
A method for manufacturing a thin film device comprising an oxide layer provided in contact with the oxide superconductor layer, wherein the oxide layer is bonded to the oxide superconductor layer or to the oxide superconductor layer by annealing. A method for producing a thin film device, characterized in that the thin film is obtained by laminating a metal thin film of an element different from the metal element contained in the oxide superconductor layer on the thin film, and then annealing the film. . 2. The oxide layer may contain some of the elements constituting the same oxide superconductor or other oxide superconductor containing Cu, an element of group II group b of the periodic table, a group III group of the periodic table. 2. The manufacturing method according to claim 1, wherein the oxide layer is substituted with a subgroup b element or a transition element other than Cu.