JPH02260475A - Formation method of Josephson junction device - Google Patents

Abstract

PURPOSE:To improve crystallinity, reproducibility and uniformity of a pattern by forming an inorganic material patterned as desired on a substrate and then forming a superconducting thin film on the substrate. CONSTITUTION:After an inorganic material 2 patterned as desired is formed on a substrate 1, a superconducting thin film 3a is formed on the substrate 1 to form a Josephson junction element. That is, a superconducting thin film 3a is formed under the same conditions on the material 2 on the substrate 1 and the substrate 1 with none of the material 2. In this case, when superconducting characteristic on the material 2 is worse than that on the substrate 1, i.e., operated as a Josephson junction element, the material 2 operates so that the superconducting thin film 3b on the inorganic material 2 hardly exhibit superconducting characteristics. Thus, a Josephson junction in which reproducibility, crystallinity, uniformly are improved can be formed.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a method for forming a Josephson junction element used in logic circuits, optical switching elements f, information recording devices, and the like.

(Prior Art) Various types of Josephson junctions have been proposed, including point contact type, sandwich type (StS type), quasi-plane type, and bridge type. Among them, the bridge type Josephson junction device has a simple structure in the element Y-form, so it is difficult to use metal superconducting thin films and B1PbBaO
Various forms of superconducting thin films have been studied.

(Japn, J. Appl, Phys., 22
．． 544 (1983), Japanese Unexamined Patent Publication No. 59-210678) [Problem to be solved by the invention] These bridge-type stain 1 Sefson junction elements are made by forming a superconducting thin film on the entire surface of the five-layer plate, and then forming a desired bridge by etching or the like. It was numerical to form. However, recently discovered ceramic superconducting thin films, such as YB
a2Cu,,07-δ6]]mirllazCu,,0
．． -δ0kuδ<1), B15rCaCu system 44
Stone has a complex material composition, and the etching rate of Y, Ba, Cu, etc. becomes W, so there is a problem that the composition of the superconductor is easily changed by etching. For this reason, it has the disadvantage that it no longer exhibits superconducting properties due to etching, and the crystallinity, reproducibility, and uniformity of the pattern are also poor.

The present invention has been made in view of the above-mentioned problems and problems of the prior art, and attempts to form a bridge-type grain boundary Sefson junction element useful for information recording devices, various logic circuits, etc. using a new bridge forming method. That is.

(11 steps to solve the f1 problem) According to the present invention, after forming an inorganic material patterned with a desired nail on a substrate, a superconducting thin film is formed on the substrate, and a Josephson junction element is formed. By forming this, a Josephson junction with improved reproducibility, crystallinity, and uniformity can be formed without increasing the etching rate.

In the present invention, the inorganic material formed in a desired pattern on the substrate 1- is a negative pattern of the superconducting thin film.

In other words, if a superconducting thin film is formed under the same conditions on a substrate on which no inorganic material is formed, as on the inorganic material of substrate 1-2, the superconducting properties of the thin film on the inorganic material will be different from those on the substrate. In other words, the inorganic material acts so that the superconducting thin film of inorganic material -F hardly exhibits superconducting properties when operated as a Josephson junction element.

This is due to atomic diffusion, lattice mismatch, and decreased crystallinity between the inorganic material and the superconducting thin film, but as a result, the critical temperature is lower than that of the superconducting thin film on the substrate, or the superconducting thin film no longer exhibits superconductivity. Therefore, the type of inorganic material is not limited as long as it satisfies this condition, but various metals, oxides, nitrides, etc. can be exemplified, and preferable ones include Al, ^u, 5in2
．． ^1203. Examples include znQ and AIN.

The inorganic material can be formed by vapor deposition using a mask, resist patterning, etc. According to these methods, it can be formed at any position 5α on the substrate E, and a desired negative pattern can be formed. can be formed.

In addition, the inorganic material pattern can be patterned to a size of 1μ or less by EBn optical patterning, etc., so the distance between each Josephson junction can be made extremely small, and the number of junctions can be increased by 1, allowing for high integration. It is also advantageous for The thickness of the inorganic material may range from several tens to several thousand pieces. In addition, although the inorganic material pattern can be formed in such a way that a desired number of Josephson junctions can be obtained, it is also possible to easily form a grain boundary Josephson junction array with high sensitivity by arranging it in a lattice pattern on the substrate. can do.

After forming a negative pattern of inorganic material as described above,
Next, by creating a superconducting thin film, a Josephson junction array can be easily formed. Further, by forming a Josephson junction array, the normal resistance value R and the superconducting critical current value IC become large, and it becomes possible to increase the electric current [fV-rcHN that can be applied to the element].

Further, the superconducting thin film to be formed may be a thin film of a superconducting material that forms grain boundary Josephson junctions, typically Y-Ba-Cu-0, B1-5r-(:a-Cu -0 etc. can be used, but the compound composition is A-B-C
- When expressed as D, A is La, Ce, Pr, or Nd.

I'm, SIa, Se, Eu, Gd, Tb,
Dy, llo, Er, Tb, Lu.

One or more elements selected from the group consisting of Tl and Y: B is one or more elements selected from the group consisting of Ba, Ca, Sr and Pb; C is V, Ti, C
r, Mr.

A thin film made of a superconducting material consisting of one or more elements selected from the group consisting of Fe, Ni, co, Ag, Cd and Cu; one or more elements selected from the group consisting of D, S and O Since it is easy to form a thin film, it is suitable for the forming method according to the present invention.

Methods for forming superconducting thin films on substrates include conventional sputtering, electron beam heating, resistance heating, MBE, C
A VD method, an ion beam method, etc. can be used, but it is preferable to use a method that can form a film under the same conditions t on the inorganic material and on the substrate. The thickness of the superconducting thin film is 100 N1.0000
About the size of a person.

Note that the superconducting thin film formed on the substrate is heat-treated if necessary, but its durability can be further improved by selecting a substrate with a coefficient of thermal expansion close to that of the superconducting thin film.

As described above, according to the bridge forming method according to the present invention, since the superconducting thin film is not subjected to processing such as film-forming etching on the substrate, the Josephson junction element obtained has good reproducibility, crystallinity, It is possible to achieve excellent uniformity and properties, and since the pattern is formed using an inorganic material rather than etching, each bond can be formed with an extremely small distance between the joints by EB exposure patterning or the like.

Cefson junctions can be formed, and highly sensitive optical switching elements, logic circuits, information recording devices, etc. can be created.

It should be noted that configurations of the present invention other than those described above can be carried out according to conventional methods.

(Examples) The present invention will be explained in more detail below with reference to Examples.

Example 1 A Josephson junction element was formed according to step 1 shown in FIGS. 1 and 2. First, a negative pattern 2 was created using an inorganic material 5i02 as a buttering material on a crystal substrate 1 (in this example, sapphire (100) was used).
figure).

On this substrate, Y -11a -(: u -0 is ICB
The film was formed using the cluster ion beam method. The film forming conditions at this time were a substrate temperature of 400°C and an oxygen partial pressure of 3 x lO.
−'Torr, and the deposition materials were Y, Bad,
The composition of substrates 1-7 was Y:Ba:Cu=1:2 by using separate cluster ion guns.
: The deposition rate was adjusted to be 3. The acceleration voltage of the cluster ion gun for Y is 1 V, the ionization current is 50 mA, the acceleration voltage of the cluster ion gun for 13aO is 05 V, the ionization current is 30 mA, the acceleration voltage for Cu is 4 KV, Ionization flow is 2
It was set to 00mA. The deposition rate is 200 layers/min and the film thickness is 5000 layers. This substrate was roughly heat treated at 940°C for 1 hour in an oxygen atmosphere to form a superconducting thin 1 model 3a.
was created (Figure 2).

Next, attach the ^U electrode and measure the resistance using liquid 11e1
However, the Y-Ba-Cu-0 thin layer 3a of sapphire 1- exhibits superconductivity with zero resistance at 70, but the Y-Ha-(:u- It was confirmed that the resistance of the 0 thin film 3b did not become 0 even at 4, did not exhibit superconductivity, and that a Josephson junction was formed.

Example 2 An Al2O1 pattern 4 was formed on a Mg0 (100) substrate by RF sputtering using a mask as shown in FIG.
20 rows and columns were created. The size of the n Al2O3 pattern 4 is 7 It m 111, and the line distance @A is 3 μm.
was fixed, and the inter-row distance B was varied from 0.5 to 2 μl to express the relationship between the clay of B and the response frequency characteristics.

This substrate J was formed by RF sputtering using a mask using a nl-5r-1:aJ:u-0 sintered target.
15! L/Takoro 1-5r-1; a-Cu-0 thin film was formed. The film forming conditions at this time are that the substrate temperature is <10
0℃, Ar gas pressure 0.5Pa, sputtering power!
Deposition speed of 50 people and 101 inches at 00W! IQ thickness is 40
There were 00 people.

This substrate was further heat-treated at 850°C for 1 hour in an oxygen atmosphere to obtain a superconducting thin 11I25 with Tc=70.
Figure 3). Table 1 shows changes in characteristics due to changes in B.

In addition, in a grain boundary Josephson junction with a weak junction of 2μ1ll×2μ■, 1c=0.2
mA, IcRm=0.18 at ItN=0.9Ω
mV, and the feltN product could be greatly improved by this development.

(Effects of the Invention) As explained above, in order to form a superconducting thin film after forming a negative pattern using an inorganic material on a single crystal substrate, grain boundary Josephson junctions can be formed by controlling the negative pattern. The 1cItN voltage of the cable array can be increased, and the voltage applied during device operation can be increased.

Furthermore, since an etching step after forming the superconducting thin film is not required, the reproducibility, crystallinity, uniformity, and properties of the device can be improved, and high-quality devices can be manufactured.

[Brief explanation of drawings]

FIG. 1 is a schematic plan view showing a configuration in which an inorganic material is formed on a substrate in the manufacturing process of the Josephson junction element f manufactured in Example 1, and FIG. FIG. 3 is a schematic plan view (partially omitted) showing the structure of the Josephson junction element fabricated in Example 2. FIG. 1: Substrate 2.4 = Inorganic material 3a, 5a: Superconducting thin film lb, 5b: Non-superconducting thin film A: Inter-row distance B: Inter-column distance

Claims (1)

[Claims] 1. In manufacturing a bridge type Josephson junction device,
After forming the inorganic material patterned as desired on the substrate,
A method for forming a Josephson junction element, comprising forming a superconducting thin film on the substrate. 2. When the compound composition of the superconducting thin film is expressed as A-B-C-D, A is La, Ce, Pr, Nd, Pm, Sm,
Sc, Eu, Gd, Tb, Dy, Ho, Er, Tm, Y
one or more elements selected from the group consisting of b, Lu, Bi, Tl and Y; B or one or more elements selected from the group consisting of Ba, Ca, Sr and Pb; C is V, Ti, C
one or more elements selected from the group consisting of r, Mn, Fe, Ni, Co, Ag, Cd and Cu; D is S and O
Claim 1 is one or more elements selected from the group consisting of
A method for forming a Josephson junction device as described in . 3. The superconducting thin film is formed under the same conditions on the inorganic material formed on the substrate and on the substrate on which the inorganic material is not formed, and the critical temperature of the superconducting thin film on the inorganic material ( 2. The method according to claim 1, wherein the superconducting transition temperature is lower than the critical temperature of the superconducting thin film on the substrate or within a range in which no superconducting state is exhibited.